Liquid crystal display device

ABSTRACT

The liquid crystal display device of the present invention includes a first substrate, a second substrate, and a vertical alignment type liquid crystal layer provided between the first substrate and the second substrate, and includes a plurality of picture element regions each defined by a first electrode provided on one side of the first substrate that is closer to the liquid crystal layer and a second electrode provided on the second substrate so as to oppose the first electrode via the liquid crystal layer. The first substrate includes a first orientation-regulating structure in each of the plurality of picture element regions, the first orientation-regulating structure exerting an orientation-regulating force so as to form a plurality of liquid crystal domains in the liquid crystal layer, each of the liquid crystal domains taking a radially-inclined orientation in the presence of an applied voltage. The second substrate includes a second orientation-regulating structure in a region corresponding to at least one of the plurality of liquid crystal domains, the second orientation-regulating structure exerting an orientation-regulating force for orienting liquid crystal molecules in at least one liquid crystal domain into a radially-inclined orientation at least in the presence of an applied voltage.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a liquid crystal display device,and more particularly to a liquid crystal display device having a wideviewing angle characteristic and being capable of producing a highquality display.

[0003] 2. Description of the Background Art

[0004] In recent years, liquid crystal display devices, which are thinand light in weight, are used as personal computer displays and PDA(personal digital assistance) displays. However, conventional twistnematic (TN) type and super twist nematic (STN) type liquid crystaldisplay devices have a narrow viewing angle. Various technicaldevelopments have been undertaken to solve the problem.

[0005] A typical technique for improving the viewing anglecharacteristic of a TN or STN type liquid crystal display device is toadd an optical compensation plate thereto. Another approach is to employa transverse electric field mode in which a horizontal electric fieldwith respect to the substrate plane is applied across the liquid crystallayer. Transverse electric field mode liquid crystal display deviceshave been attracting public attention and are mass-produced in recentyears. Still another technique is to employ a DAP (deformation ofvertical aligned phase) mode in which a nematic liquid crystal materialhaving a negative dielectric anisotropy is used as a liquid crystalmaterial and a vertical alignment film is used as an alignment film.This is a type of ECB (electrically controlled birefringence) mode, inwhich the transmittance is controlled by using the birefringence ofliquid crystal molecules.

[0006] While the transverse electric field mode is an effective approachto improve the viewing angle, the production process thereof imposes asignificantly lower production margin than that of a normal TN typedevice, whereby it is difficult to realize stable production of thedevice. This is because the display brightness or the contrast ratio issignificantly influenced by variations in the gap between the substratesor a shift in the direction of the transmission axis (polarization axis)of a polarization plate with respect to the orientation axis of theliquid crystal molecules. It requires further technical developments tobe able to precisely control these factors and thus to realize stableproduction of the device.

[0007] In order to realize a uniform display without displaynon-uniformity with a DAP mode liquid crystal display device, analignment control is necessary. An alignment control can be provided by,for example, subjecting the surface of an alignment film to an alignmenttreatment by rubbing. However, when a vertical alignment film issubjected to a rubbing treatment, rubbing streaks are likely to appearin the displayed image, and it is not suitable for mass-production.

[0008] Another approach proposed in the art for performing an alignmentcontrol without a rubbing treatment is to form a slit (opening) in anelectrode so as to produce an inclined electric field and to control theorientation direction of the liquid crystal molecules by the inclinedelectric field (e.g., Japanese Laid-Open Patent Publication Nos.6-301036 and 2000-47217). However, the present inventors reviewed thesepublications and found that with the methods disclosed therein, theorientation in regions of the liquid crystal layer corresponding to theopenings in the electrode is not defined, whereby the orientation of theliquid crystal molecules is not sufficiently continuous, and it isdifficult to achieve a stable orientation across each pixel, resultingin a display with non-uniformity.

SUMMARY OF THE INVENTION

[0009] The present invention has been made to solve these problems inthe prior art, and has an object to provide a liquid crystal displaydevice having a wide viewing angle characteristic and a high displayquality.

[0010] A liquid crystal display device of the present inventionincludes: a first substrate, a second substrate, and a verticalalignment type liquid crystal layer provided between the first substrateand the second substrate; and a plurality of picture element regionseach defined by a first electrode provided on one side of the firstsubstrate that is closer to the liquid crystal layer and a secondelectrode provided on the second substrate so as to oppose the firstelectrode via the liquid crystal layer, wherein: the first substrateincludes a first orientation-regulating structure in each of theplurality of picture element regions, the first orientation-regulatingstructure exerting an orientation-regulating force so as to form aplurality of liquid crystal domains in the liquid crystal layer, each ofthe liquid crystal domains taking a radially-inclined orientation in thepresence of an applied voltage; and the second substrate includes asecond orientation-regulating structure in a region corresponding to atleast one of the plurality of liquid crystal domains, the secondorientation-regulating structure exerting an orientation-regulatingforce for orienting liquid crystal molecules in the at least one liquidcrystal domain into a radially-inclined orientation at least in thepresence of an applied voltage. Thus, the object set forth above isachieved.

[0011] Preferably, the second orientation-regulating structure isprovided in a region corresponding to a region in the vicinity of acenter of the at least one liquid crystal domain.

[0012] Preferably, in the at least one liquid crystal domain, adirection of orientation regulation by the second orientation-regulatingstructure coincides with a direction of the radially-inclinedorientation by the first orientation-regulating structure.

[0013] The first electrode may include a plurality of unit solidportions, the first orientation-regulating structure including theplurality of unit solid portions, so that when a voltage is appliedbetween the first electrode and the second electrode, an inclinedelectric field is produced along a periphery of each of the plurality ofunit solid portions, thereby forming the plurality of liquid crystaldomains in regions respectively corresponding to the plurality of unitsolid portions.

[0014] Preferably, a shape of each of the plurality of unit solidportions has rotational symmetry. Preferably, the plurality of unitsolid portions are arranged so as to have rotational symmetry in eachpicture element region.

[0015] Each of the plurality of unit solid portions may have a shapewith an acute angle corner.

[0016] The first electrode may include at least one opening and a solidportion; and the first orientation-regulating structure may include theat least one opening and the solid portion of the first electrode, sothat when a voltage is applied between the first electrode and thesecond electrode, an inclined electric field is produced at an edgeportion of the at least one opening of the first electrode, therebyforming the plurality of liquid crystal domains in regions respectivelycorresponding to the at least one opening and the solid portion.

[0017] The first substrate may further include a dielectric layerprovided on one side of the first electrode that is away from the liquidcrystal layer, and a third electrode opposing at least a portion of theat least one opening of the first electrode via the dielectric layer.

[0018] Preferably, the at least one opening includes a plurality ofopenings having substantially the same shape and substantially the samesize, and at least some of the plurality of openings form at least oneunit lattice arranged so as to have rotational symmetry. Preferably, ashape of each of the at least some of the plurality of openings hasrotational symmetry.

[0019] The second orientation-regulating structure may be provided in aregion corresponding to each of the plurality of liquid crystal domains.Alternatively, the second orientation-regulating structure may beprovided only in a region corresponding to one or more of the pluralityof liquid crystal domains that is formed in a region corresponding tothe solid portion of the first electrode.

[0020] The second orientation-regulating structure may exert anorientation-regulating force for orienting the liquid crystal moleculesinto a radially-inclined orientation even in the absence of an appliedvoltage. For example, the second orientation-regulating structure may bea protrusion protruding from the second substrate into the liquidcrystal layer. A thickness of the liquid crystal layer may be defined bythe protrusion protruding from the second substrate into the liquidcrystal layer. Preferably, the protrusion includes a side surface at anangle less than 90° with respect to a substrate plane of the secondsubstrate. Alternatively, the second orientation-regulating structuremay include a surface having a horizontal alignment power provided onone side of the second substrate that is closer to the liquid crystallayer.

[0021] The second orientation-regulating structure may exert anorientation-regulating force for orienting the liquid crystal moleculesinto a radially-inclined orientation only in the presence of an appliedvoltage. For example, the second orientation-regulating structure mayinclude an opening provided in the second electrode.

[0022] Another liquid crystal display device of the present inventionincludes: a first substrate, a second substrate, and a verticalalignment type liquid crystal layer provided between the first substrateand the second substrate; and a plurality of picture element regionseach defined by a first electrode provided on one side of the firstsubstrate that is closer to the liquid crystal layer and a secondelectrode provided on the second substrate so as to oppose the firstelectrode via the liquid crystal layer, wherein: the first electrodeincludes, in each of the plurality of picture element regions, aplurality of openings and a plurality of unit solid portions, each ofthe unit solid portions being surrounded by at least some of theplurality of openings; and the second substrate includes anorientation-regulating structure in a region corresponding to at leastone unit solid portion among the plurality of unit solid portions andthe plurality of openings. Thus, the object set forth above is achieved.

[0023] Preferably, a shape of each of the plurality of unit solidportions has rotational symmetry. Preferably, the plurality of unitsolid portions are arranged so as to have rotational symmetry in eachpicture element region.

[0024] Preferably, the orientation-regulating structure is provided in aregion corresponding to a region in the vicinity of a center of the atleast one of the plurality of unit solid portions and the plurality ofopenings.

[0025] The orientation-regulating structure may be a protrusionprotruding from the second substrate into the liquid crystal layer. Athickness of the liquid crystal layer may be defined by the protrusionprotruding from the second substrate into the liquid crystal layer.Preferably, the protrusion includes a side surface at an angle less than90° with respect to a substrate plane of the second substrate.

[0026] The orientation-regulating structure may include a surface havinga horizontal alignment power provided on one side of the secondsubstrate that is closer to the liquid crystal layer.

[0027] The orientation-regulating structure may include an openingprovided in the second electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1A and FIG. 1B schematically illustrate a structure of onepicture element region of a liquid crystal display device 100 having afirst orientation-regulating structure of the present invention, wherein

[0029]FIG. 1A is a plan view, and

[0030]FIG. 1B is a cross-sectional view taken along line 1B-1B′ of FIG.1A.

[0031]FIG. 2A and FIG. 2B illustrate a liquid crystal layer 30 of theliquid crystal display device 100 in the presence of an applied voltagethereacross, wherein

[0032]FIG. 2A schematically illustrates a state where an orientation hasjust started to change (initial ON state), and

[0033]FIG. 2B schematically illustrates a steady state.

[0034] Each of FIG. 3A to FIG. 3D schematically illustrates therelationship between an electric force line and an orientation of aliquid crystal molecule.

[0035] Each of FIG. 4A to FIG. 4C schematically illustrates anorientation of liquid crystal molecules in the liquid crystal displaydevice 100 as viewed in a substrate normal direction.

[0036]FIG. 5A to FIG. 5C schematically illustrate exemplaryradially-inclined orientations of liquid crystal molecules.

[0037]FIG. 6A and FIG. 6B are plan views schematically illustratingother picture element electrodes used in the liquid crystal displaydevice of the present invention.

[0038]FIG. 7A and FIG. 7B are plan views schematically illustratingstill other picture element electrodes used in the liquid crystaldisplay device of the present invention.

[0039]FIG. 8AFIG. 8B are plan views schematically illustrating stillother picture element electrodes used in the liquid crystal displaydevice of the present invention.

[0040]FIG. 9A and FIG. 9B are plan views schematically illustratingstill other picture element electrodes used in the liquid crystaldisplay device of the present invention.

[0041]FIG. 10A and FIG. 10B are plan views each schematicallyillustrating a corner of a unit solid portion of a picture elementelectrode used in the liquid crystal display device of the presentinvention.

[0042]FIG. 11A is a graph illustrating a change in the transmittancewith respect to the angle of a polarization axis of a polarization platein a liquid crystal display device having a picture element electrodeillustrated in FIG. 8B and in a liquid crystal display device having apicture element electrode illustrated in FIG. 9B, and

[0043]FIG. 11B schematically illustrates an arrangement of thepolarization axis corresponding to 0°.

[0044]FIG. 12 is a plan view schematically illustrating still anotherpicture element electrode used in the liquid crystal display device ofthe present invention.

[0045]FIG. 13A and FIG. 13B are plan views schematically illustratingstill other picture element electrodes used in the liquid crystaldisplay device of the present invention.

[0046]FIG. 14A schematically illustrates a unit lattice of the patternillustrated in FIG. 1A,

[0047]FIG. 14B schematically illustrates a unit lattice of the patternillustrated in FIG. 12, and

[0048]FIG. 14C is a graph illustrating the relationship between a pitchp and a solid portion area ratio.

[0049]FIG. 15A and FIG. 15B schematically illustrate a structure of onepicture element region of a liquid crystal display device 200 having afirst orientation-regulating structure of the present invention, wherein

[0050]FIG. 15A is a plan view, and

[0051]FIG. 15B is a cross-sectional view taken along line 15B-15B′ ofFIG. 15A.

[0052]FIG. 16A to FIG. 16D schematically illustrate the relationshipbetween an orientation of liquid crystal molecules 30 a and a surfaceconfiguration having a vertical alignment power.

[0053]FIG. 17A and FIG. 17B illustrate a state in the presence of anapplied voltage across a liquid crystal layer 30 of the liquid crystaldisplay device 200, wherein

[0054]FIG. 17A schematically illustrates a state where an orientationhas just started to change (initial ON state), and

[0055]FIG. 17B schematically illustrates a steady state.

[0056]FIG. 18A to FIG. 18C are cross-sectional views schematicallyillustrating liquid crystal display devices 200A, 200B and 200C,respectively, having different positional relationships between anopening and a protrusion.

[0057]FIG. 19 is a cross-sectional view schematically illustrating theliquid crystal display device 200 taken along line 19A-19A′ of FIG. 15A.

[0058]FIG. 20A and FIG. 20B schematically illustrate a structure of onepicture element region of a liquid crystal display device 200D, wherein

[0059]FIG. 20A is a plan view, and

[0060]FIG. 20B is a cross-sectional view taken along line 20B-20B′ ofFIG. 20A.

[0061]FIG. 21A to FIG. 21C are cross-sectional views schematicallyillustrating one picture element region of a liquid crystal displaydevice 300 having a two-layer electrode, wherein

[0062]FIG. 21A illustrates a state in the absence of an applied voltage,

[0063]FIG. 21B illustrates a state where an orientation has just startedto change (initial ON state), and

[0064]FIG. 21C illustrates a steady state.

[0065]FIG. 22A to FIG. 22C are cross-sectional views schematicallyillustrating one picture element region of another liquid crystaldisplay device 400 having a two-layer electrode, wherein

[0066]FIG. 22A illustrates a state in the absence of an applied voltage,

[0067]FIG. 22B illustrates a state where an orientation has just startedto change (initial ON state), and

[0068]FIG. 22C illustrates a steady state.

[0069]FIG. 23 is a cross-sectional view schematically illustrating onepicture element region of still another liquid crystal display device500 having a two-layer electrode.

[0070]FIG. 24A to FIG. 24E each schematically illustrate a countersubstrate 600 b including a second orientation-regulating structure 28.

[0071]FIG. 25A and FIG. 25B schematically illustrate a liquid crystaldisplay device 600 including a first orientation-regulating structureand a second orientation-regulating structure, wherein

[0072]FIG. 25A is a plan view, and

[0073]FIG. 25B is a cross-sectional view taken along line 25B-25B′ ofFIG. 25A.

[0074]FIG. 26A to FIG. 26C are cross-sectional views schematicallyillustrating one picture element region of the liquid crystal displaydevice 600, wherein

[0075]FIG. 26A illustrates a state in the absence of an applied voltage,

[0076]FIG. 26B illustrates a state where an orientation has just startedto change (initial ON state), and

[0077]FIG. 26C illustrates a steady state.

[0078]FIG. 27A and FIG. 27B schematically illustrate another liquidcrystal display device 700 including a first orientation-regulatingstructure and a second orientation-regulating structure, wherein

[0079]FIG. 27A is a plan view, and

[0080]FIG. 27B is a cross-sectional view taken along line 27B-27B′ ofFIG. 27A.

[0081]FIG. 28A to FIG. 28C are cross-sectional views schematicallyillustrating one picture element region of the liquid crystal displaydevice 700, wherein

[0082]FIG. 28A illustrates a state in the absence of an applied voltage,

[0083]FIG. 28B illustrates a state where an orientation has just startedto change (initial ON state), and

[0084]FIG. 28C illustrates a steady state.

[0085]FIG. 29A to FIG. 29C are cross-sectional views schematicallyillustrating one picture element region of still another liquid crystaldisplay device 800 including a first orientation-regulating structureand a second orientation-regulating structure, wherein

[0086]FIG. 29A illustrates a state in the absence of an applied voltage,

[0087]FIG. 29B illustrates a state where an orientation has just startedto change (initial ON state), and

[0088]FIG. 29C illustrates a steady state.

[0089]FIG. 30A and FIG. 30B schematically illustrate a liquid crystaldisplay device 900 including a protrusion that functions as a spacer,wherein

[0090]FIG. 30A is a plan view, and

[0091]FIG. 30B is a cross-sectional view taken along line 30B-30B′ ofFIG. 30A.

[0092]FIG. 31A to FIG. 31C are cross-sectional views schematicallyillustrating one picture element region of the liquid crystal displaydevice 900, wherein

[0093]FIG. 31A illustrates a state in the absence of an applied voltage,

[0094]FIG. 31B illustrates a state where an orientation has just startedto change (initial ON state), and

[0095]FIG. 31C illustrates a steady state.

[0096]FIG. 32 is a cross-sectional view schematically illustrating aprotrusion having a side surface whose inclination angle with respect tothe substrate plane is 90° or more.

[0097]FIG. 33 is a cross-sectional view schematically illustrating avariation of a protrusion that functions as a spacer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0098] First, the basic function of each element of a liquid crystaldisplay device of the present invention will be described.

[0099] The liquid crystal display device of the present inventionincludes a pair of substrates that are arranged with a verticalalignment type liquid crystal layer being interposed therebetween. Oneof the pair of substrates has a first orientation-regulating structurecapable of exerting an orientation-regulating force such that aplurality of liquid crystal domains are formed in each picture elementregion, each liquid crystal domain taking a radially-inclinedorientation (referred to also as an “axially symmetrical orientation”)in the presence of an applied voltage. The other substrate has a secondorientation-regulating structure capable of exerting anorientation-regulating force such that the liquid crystal molecules arearranged in a radially-inclined orientation at least in the presence ofan applied voltage, in a region corresponding to at least one of theliquid crystal domains. Therefore, the orientation-regulating force fromthe first orientation-regulating structure and that from the secondorientation-regulating structure act upon the liquid crystal moleculesat least in the presence of an applied voltage, whereby theradially-inclined orientation of each liquid crystal domain formed inthe liquid crystal layer is more stable than that in a case where onlythe first orientation-regulating structure is provided.

[0100] A preferred first orientation-regulating structure of the liquidcrystal display device of the present invention includes one of a pairof electrodes for applying a voltage across the liquid crystal layer ineach picture element region. The electrode includes a plurality of unitsolid portions so that an inclined electric field is produced along theperiphery of each of the unit solid portions upon application of avoltage between the pair of electrodes, thereby forming a plurality ofliquid crystal domains in regions corresponding to the unit solidportions, respectively. The outer shape of the electrode is defined sothat upon application of a voltage between the pair of electrodes, aninclined electric field is produced around the electrode so as to form aplurality of liquid crystal domains each taking a radially-inclinedorientation.

[0101] Herein, a portion of an electrode where a conductive film exitsis referred to as a “solid portion”, and a portion of the solid portionthat produces an electric field for forming a single liquid crystaldomain is referred to as a “unit solid portion”. Each solid portion istypically made of a continuous conductive film.

[0102] It is preferred that the shape of each of the unit solid portionshas rotational symmetry. When the shape of the unit solid portion hasrotational symmetry, the resulting liquid crystal domain will also be ina radially-inclined orientation having rotational symmetry, i.e., anaxially symmetrical orientation, thereby improving the viewing anglecharacteristic.

[0103] Another preferred first orientation-regulating structure of theliquid crystal display device of the present invention is an electrodestructure in which one of the pair of electrodes for applying a voltageacross the liquid crystal layer in each picture element region has atleast one opening (a portion of the electrode where the conductive filmdoes not exist) and a solid portion (a portion of the electrode otherthan the opening, i.e., a portion where a conductive film exists). Thesolid portion typically includes at least one unit solid portion asdescribed above. By providing openings in one of the electrodes, it ispossible to form a number of (e.g., four) unit solid portions that aretwo-dimensionally arranged in one picture element region. In this way,it is possible to form a larger number of liquid crystal domains than ina case where a number of (e.g., two) unit solid portions are formed bydefining the outer shape of the electrode to be a predetermined shapewithout forming openings in the electrode.

[0104] Note that while openings can be formed so that a liquid crystaldomain taking a radially-inclined orientation is also formed in a regioncorresponding to an electrode opening, as will be described later, thismay not be necessary. As long as a liquid crystal domain taking aradially-inclined orientation is formed so as to correspond to the solidportion (unit solid portion), a continuity of the orientation of theliquid crystal molecules in each picture element region is ensured,thereby stabilizing the radially-inclined orientation of the liquidcrystal domain formed so as to correspond to the solid portion, evenwhen a liquid crystal domain formed so as to correspond to an openingdoes not take a radially-inclined orientation. Particularly, when thearea of an opening is small, the opening has only a little contributionto the display, and thus the display quality will not deterioratesignificantly even if a liquid crystal domain taking a radially-inclinedorientation is not formed in a region corresponding to the opening.

[0105] A plurality of liquid crystal domains are formed in the liquidcrystal layer. Each liquid crystal domain takes a vertical alignment inthe absence of an applied voltage, and takes a radially-inclinedorientation in the presence of an applied voltage due to an inclinedelectric field that is produced at an edge portion of the electrodeopening. A vertical alignment type liquid crystal layer is a liquidcrystal layer in which the liquid crystal molecules are aligned in adirection substantially perpendicular to the substrate plane in theabsence of an applied voltage. Typically, a vertical alignment typeliquid crystal layer is made of a liquid crystal material having anegative dielectric anisotropy, and the orientation is regulated byvertical alignment films provided on the opposing sides.

[0106] When a voltage is applied between the pair of electrodes, aninclined electric field is produced in the vertical alignment typeliquid crystal layer, thereby forming liquid crystal domains in regionscorresponding to openings and solid portions of the electrode. Imagesare displayed by changing the orientation of the liquid crystal domainsaccording to the applied voltage. Since each liquid crystal domain takesa radially-inclined orientation (axially symmetrical orientation), thereis little viewing angle dependence of the display quality and thus awide viewing angle characteristic.

[0107] Moreover, a liquid crystal domain corresponding to an opening anda liquid crystal domain corresponding to a solid portion are both formedby an inclined electric field produced at the edge portion of theopening, whereby these liquid crystal domains are formed adjacent toeach other in an alternating pattern, and the orientation of the liquidcrystal molecules in one liquid crystal domain and that in anotheradjacent liquid crystal domain are essentially continuous with eachother. Therefore, no disclination line is formed between a liquidcrystal domain formed in an opening and another adjacent liquid crystaldomain formed in a solid portion, whereby the display quality is notdeteriorated and the orientation of the liquid crystal molecules ishighly stable.

[0108] When a liquid crystal display device employs an electrodestructure as described above, the liquid crystal molecules take aradially-inclined orientation not only in a region corresponding to anelectrode solid portion but also in a region corresponding to anopening. With such a liquid crystal display device, as compared to theconventional liquid crystal display device described above, thecontinuity in the orientation of the liquid crystal molecules is higherwhile a stable orientation is realized and a uniform display withoutdisplay non-uniformity can be obtained. Particularly, in order torealize a desirable response characteristic (high response speed), aninclined electric field for controlling the orientation of the liquidcrystal molecules needs to act upon a large number of liquid crystalmolecules. For this purpose, it is necessary to form a large number ofopenings (edge portions). In the liquid crystal display device of thepresent invention, a liquid crystal domain having a stableradially-inclined orientation is formed corresponding to an opening.Therefore, even if a large number of openings are formed in order toimprove the response characteristic, a decrease in the display quality(occurrence of display non-uniformity) can be suppressed.

[0109] When at least some of the openings are provided to form at leastone unit lattice arranged so as to have rotational symmetry withsubstantially the same shape and substantially the same size, aplurality of liquid crystal domains can be arranged with a high degreeof symmetry for each unit lattice, whereby it is possible to improve theviewing angle dependence of the display quality. Moreover, by dividingthe entire picture element region into unit lattices, it is possible tostabilize the orientation of the liquid crystal layer across the entirepicture element region. For example, openings may be arranged so thatthe centers of the openings form a square lattice. Note that where eachpicture element region is divided by an opaque element such as a storagecapacitance line, a unit lattice can be arranged for each regioncontributing to the display.

[0110] When at least some of the openings (typically those forming aunit lattice) each have a shape having rotational symmetry, it ispossible to increase the stability of the radially-inclined orientationof the liquid crystal domain formed in the opening. For example, theshape of each opening (as viewed in the substrate normal direction) maybe a circular shape or a polygonal shape (e.g., a square shape). Notethat a shape that does not have rotational symmetry (e.g., an ellipticalshape) may be employed depending upon the shape (aspect ratio) of thepicture element, etc. Moreover, when the shape of a region of the solidportion that is substantially surrounded by the openings (“unit solidportion”) has rotational symmetry, it is possible to increase thestability of the radially-inclined orientation of the liquid crystaldomain formed in the solid portion. For example, when the openings arearranged in a square lattice pattern, the shape of the opening may be agenerally star shape or a cross shape, and the shape of the solidportion may be a generally circular shape, a generally square shape, orthe like. Of course, the openings and the solid portion substantiallysurrounded by the openings may both have a generally square shape.

[0111] In order to stabilize the radially-inclined orientation of theliquid crystal domain formed in the electrode opening, it is preferredthat the liquid crystal domain formed in the opening has a generallycircular shape. In other words, the shape of the opening may be designedso that the liquid crystal domain formed in the opening has a generallycircular shape.

[0112] Of course, in order to stabilize the radially-inclinedorientation of the liquid crystal domain formed in the electrode solidportion, it is preferred that the region of the solid portionsubstantially surrounded by the openings has a generally circular shape.A liquid crystal domain formed in the solid portion, which is made of acontinuous conductive film, is formed corresponding to a region of asolid portion (unit solid portion) that is substantially surrounded by aplurality of openings. Therefore, the shape and arrangement of theopenings may be determined so that the region of the solid portion (unitsolid portion) has a generally circular shape.

[0113] With any of the alternatives described above, it is preferredthat the total area of the openings formed in the electrode is smallerthan the area of the solid portion in each picture element region. Asthe area of the solid portion increases, the area of the liquid crystallayer (defined in the plane of the liquid crystal layer as viewed in thesubstrate normal direction) that is directly influenced by the electricfield produced by the electrodes increases, thereby improving theoptical characteristics (e.g., the transmittance) with respect to thevoltage applied across the liquid crystal layer.

[0114] It is preferred that whether to employ an arrangement where eachopening has a generally circular shape or an arrangement where each unitsolid portion has a generally circular shape is determined bydetermining with which arrangement, the area of the solid portion can bemade larger. Which arrangement is more preferred is appropriatelyselected depending upon the pitch of the picture elements. Typically,when the pitch is greater than about 25 Am, it is preferred that theopenings are formed so that each solid portion has a generally circularshape. When the pitch is less than or equal to about 25 μm, it ispreferred that each opening has a generally circular shape.

[0115] With the electrode arrangement where openings are provided in oneof a pair of electrodes, a sufficient voltage may not be applied acrossthe liquid crystal layer in a region corresponding to the opening and asufficient retardation change may not be obtained, thereby decreasingthe light efficiency. In view of this, a dielectric layer may beprovided on one side of the electrode with openings that is away fromthe liquid crystal layer, with an additional electrode being providedvia the dielectric layer so as to at least partially oppose theelectrode openings (i.e., a two-layer electrode may be employed). Inthis way, it is possible to apply a sufficient voltage across the liquidcrystal layer corresponding to the opening, thereby improving the lightefficiency and/or the response characteristic.

[0116] Where the electrode structure described above (i.e., the firstorientation-regulating structure) is only provided in one of thesubstrates, if the radially-inclined orientation is disturbed by astress acting upon the liquid crystal layer, the disturbed orientationmay be maintained by the electric field effect and thus is observed asan after image phenomenon. However, the liquid crystal display device ofthe present invention includes a second orientation-regulating structurein the other substrate, in addition to the first orientation-regulatingstructure, whereby the orientation-regulating force from the firstorientation-regulating structure and that from the secondorientation-regulating structure act upon the liquid crystal moleculesin each liquid crystal domain at least in the presence of an appliedvoltage. Therefore, the radially-inclined orientation of the liquidcrystal domain is stabilized and the decrease in the display quality dueto a stress is suppressed, as compared with an arrangement having onlythe first orientation-regulating structure.

[0117] When the second orientation-regulating structure is provided in aregion in the vicinity of the center of a liquid crystal domain taking aradially-inclined orientation that is formed by the firstorientation-regulating structure, it is possible to fix the position ofthe central axis of the radially-inclined orientation, therebyeffectively improving the resistance of the radially-inclinedorientation to a stress.

[0118] When the orientation-regulating direction of the secondorientation-regulating structure may be set in conformity with thedirection of the radially-inclined orientation by the firstorientation-regulating structure. In this way, the continuity andstability of the orientation increase, thereby improving the displayquality and the response characteristic.

[0119] While the second orientation-regulating structure provides effectof stabilizing the orientation as long as it exerts anorientation-regulating force at least in the presence of an appliedvoltage, the orientation can be stabilized irrespective of the level ofthe applied voltage if an arrangement that exerts anorientation-regulating force also in the absence of an applied voltageis employed. However, since a vertical alignment type liquid crystallayer in which the liquid crystal molecules are aligned substantiallyvertical to the substrate plane in the absence of an applied voltage isemployed, the display quality may decrease if a secondorientation-regulating structure that exerts an orientation-regulatingforce also in the absence of an applied voltage is employed. However,since the orientation-regulating force of the secondorientation-regulating structure is effective even if it is relativelyweak, as will be described later, the orientation can be sufficientlystabilized even with a structure that is small with respect to the sizeof each picture element, and the decrease in the display quality in theabsence of an applied voltage may be insignificant in some cases.Depending upon the application of the liquid crystal display device(e.g., the magnitude of the externally applied stress) and/or theelectrode arrangement (the strength of the orientation-regulating forceprovided by the first orientation-regulating structure), a secondorientation-regulating structure that exerts a relatively strongorientation-regulating force may be provided. In such a case, alight-blocking layer may be provided in order to suppress the decreasein the display quality due to the second orientation-regulatingstructure.

[0120] Moreover, the radially-inclined orientation of each liquidcrystal domain can be stabilized as long as the orientation-regulatingforce by the second orientation-regulating structure acts upon thoseliquid crystal molecules in each liquid crystal domain taking aradially-inclined orientation that is formed by the firstorientation-regulating structure. Particularly, when the secondorientation-regulating structure is provided in a region in the vicinityof the center of a liquid crystal domain, an effect of fixing theposition of the central axis of the radially-inclined orientation isalso obtained. The second orientation-regulating structure may berealized by using any of various structures because it is only requiredto exert an orientation-regulating force weaker than that exerted by thefirst orientation-regulating structure.

[0121] When an electrode structure with openings as described above isemployed as the first orientation-regulating structure, liquid crystaldomains are formed both in the openings and in the solid portion. Byproviding the second orientation-regulating structure for each of theliquid crystal domains to be formed, it is possible to stabilize theradially-inclined orientation of each liquid crystal domain. However, apractically sufficient stability (stress resistance) can be obtained byproviding the second orientation-regulating structures only for thoseliquid crystal domains that are formed corresponding to the solidportion.

[0122] Particularly, a second orientation-regulating structure thatexerts an orientation-regulating force in conformity with theradially-inclined orientation formed in the electrode solid portion ismore preferable in terms of the production efficiency because it can beprovided by a simpler process as compared to a secondorientation-regulating structure that exerts an orientation-regulatingforce in conformity with the radially-inclined orientation formed in theelectrode opening. Moreover, while it is preferred that the secondorientation-regulating structure is provided for each of the unit solidportions, a practical orientation stability may be obtained by providingthe second orientation-regulating structure only for some of the unitsolid portions depending upon the electrode structure (the number andarrangement of openings). This is because in the liquid crystal displaydevice of the present invention, the radially-inclined orientationsformed in the liquid crystal layer are essentially continuous with oneanother.

[0123] Moreover, in order to improve the resistance to a stress, aprotrusion including a side surface that gives the liquid crystalmolecules of the liquid crystal layer an orientation-regulating force ofthe same direction as the orientation-regulating direction of theinclined electric field described above may be provided inside theelectrode opening. It is preferred that the cross-sectional shape of theprotrusion in the substrate plane direction is the same as the shape ofthe opening and has rotational symmetry as the shape of the openingdescribed above. However, since the liquid crystal molecules whoseorientation is regulated by the orientation-regulating force of the sidesurface of the protrusion have a poor response to an applied voltage (asmall retardation change in response to the applied voltage), theprotrusion may decrease the contrast ratio of the display. Therefore, itis preferred that the size, the height and the number of protrusions areset so as not to decrease the display quality.

[0124] Of the electrode structures that function as the firstorientation-regulating structure of the liquid crystal display device ofthe present invention, the electrode having the openings as describedabove is, for example, a picture element electrode connected to aswitching element in an active matrix type liquid crystal display deviceincluding a switching element such as a TFT in each picture elementregion, while the other electrode is at least one counter electrodeopposing a plurality of picture element electrodes. Thus, by providingopenings only in one of a pair of electrodes provided so as to opposeeach other via the liquid crystal layer, it is possible to realize astable radially-inclined orientation. Specifically, with a productionmethod known in the art, it is possible to produce a liquid crystaldisplay device having the first orientation-regulating structure only bymodifying a photomask used in the process of patterning a conductivefilm into the shape of the picture element electrode so that openingshaving an intended shape are formed in an intended arrangement. Ofcourse, a plurality of openings may be provided in the counterelectrode. Moreover, a two-layer electrode as described above may beproduced by using a method known in the art.

[0125] Moreover, the second orientation-regulating structure of theliquid crystal display device of the present invention is, for example,a protrusion protruding from the counter substrate into the liquidcrystal layer. Alternatively, the second orientation-regulatingstructure may be a structure having a horizontal alignment type surfaceprovided on one side of the counter substrate that is closer to theliquid crystal layer. Alternatively, the second orientation-regulatingstructure may be an opening provided in the counter electrode. Thesestructures may be produced by a method known in the art.

[0126] Moreover, the liquid crystal display device of the presentinvention may have an arrangement such that one of a pair of substratesarranged so as to interpose a vertical alignment type liquid crystallayer therebetween (“first substrate”) includes an electrode having aplurality of unit solid portions and a plurality of openings in eachpicture element region, with the other substrate (“second substrate”)including an orientation-regulating structure in at least one regioncorresponding to a unit solid portion among a plurality of unit solidportions and a plurality of openings.

[0127] The electrode of the first substrate is such that an inclinedelectric field is produced along the periphery of each of the unit solidportions upon application of a voltage between the electrode and theelectrode of the second substrate, thereby forming a plurality of liquidcrystal domains each taking a radially-inclined orientation in regionscorresponding to the unit solid portions, respectively. Of course, theelectrode may be configured so that a liquid crystal domain taking aradially-inclined orientation is formed also in each regioncorresponding to the electrode opening. This electrode structurefunctions similarly to the first orientation-regulating structuredescribed above. A preferred arrangement of this electrode structure issubstantially the same as that of the first orientation-regulatingstructure described above. For example, the shape of each of the unitsolid portions preferably has rotational symmetry, and the unit solidportions are preferably arranged so that they have rotational symmetryin each picture element region.

[0128] In a liquid crystal display device in which one of the substratesincludes an electrode having such a structure as described above whilethe other substrate includes an orientation-regulating structure, theorientation-regulating force from the above-described electrodestructure and that from the orientation-regulating structure act uponthe liquid crystal molecules in each liquid crystal domain at least inthe presence of an applied voltage. Therefore, the radially-inclinedorientation of the liquid crystal domain is stabilized and the decreasein the display quality due to a stress is suppressed.

[0129] The orientation-regulating structure functions substantiallysimilarly to the second orientation-regulating structure as describedabove. A preferred arrangement of this orientation-regulating structureis substantially the same as that of the second orientation-regulatingstructure described above. For example, by providing theorientation-regulating structure in a region in the vicinity of thecenter of each liquid crystal domain taking a radially-inclinedorientation that is formed in the unit solid portion or the opening ofthe electrode, it is possible to fix the position of the central axis ofthe radially-inclined orientation, thereby effectively improving theresistance of the radially-inclined orientation to a stress. Theorientation-regulating structure may be a protrusion protruding from thesecond substrate into the liquid crystal layer. Alternatively, theorientation-regulating structure may be a structure having a horizontalalignment layer provided on one side of the second substrate that iscloser to the liquid crystal layer. Alternatively, theorientation-regulating structure may be an opening provided in theelectrode of the second substrate.

[0130] A liquid crystal display device according to an embodiment of thepresent invention will now be described with reference to the drawings.

[0131] First Orientation-regulating Structure

[0132] First, a first orientation-regulating structure, which is apreferred electrode structure for the liquid crystal display device ofthe present invention, and a function thereof will be described.

[0133] The liquid crystal display device of the present invention hasdesirable display characteristics and thus can be suitably used as anactive matrix type liquid crystal display device. An embodiment of thepresent invention will now be described with respect to an active matrixtype liquid crystal display device using thin film transistors (TFTs).Note, however, that the present invention is not limited thereto, butmay alternatively be used with an MIM active matrix type liquid crystaldisplay device or a passive matrix type liquid crystal display device.Moreover, while the embodiment of the present invention will bedescribed with respect to a transmission type liquid crystal displaydevice, the present invention is not limited thereto, but mayalternatively be used with a reflection type liquid crystal displaydevice or even a transmission-reflection liquid crystal display deviceto be described later.

[0134] In the present specification, a region of a liquid crystaldisplay device corresponding to a “picture element”, which is theminimum unit of display, will be referred to as a “picture elementregion”. In a color liquid crystal display device, R, G and B “pictureelements” correspond to one “pixel”. In an active matrix type liquidcrystal display device, a picture element region is defined by a pictureelement electrode and a counter electrode which opposes the pictureelement electrode. In a passive matrix type liquid crystal displaydevice, a picture element region is defined as a region where one ofcolumn electrodes which are arranged in a stripe pattern crosses one ofrow electrodes which are also arranged in a stripe pattern perpendicularto the column electrodes. In an arrangement with a black matrix,strictly speaking, a picture element region is a portion of each regionacross which a voltage is applied according to the intended displaystate which corresponds to an opening of the black matrix.

[0135] A structure of one picture element region of a liquid crystaldisplay device 100 having a first orientation-regulating structure ofthe present invention will be described with reference to FIG. 1A andFIG. 1B. In the following description, a color filter and a black matrixare omitted for the sake of simplicity. Moreover, in subsequent figures,each element having substantially the same function as the correspondingelement in the liquid crystal display device 100 will be denoted by thesame reference numeral and will not be further described below. FIG. 1Ais a plan view as viewed in the substrate normal direction, and FIG. 1Bis a cross-sectional view taken along line 1B-1B′ of FIG. 1A. FIG. 1Billustrates a state where no voltage is applied across a liquid crystallayer.

[0136] The liquid crystal display device 100 includes an active matrixsubstrate (hereinafter referred to as a “TFT substrate”) 100 a, acounter substrate (referred to also as a “color filter substrate”) 100b, and a liquid crystal layer 30 provided between the TFT substrate 100a and the counter substrate 100 b. Liquid crystal molecules 30 a of theliquid crystal layer 30 have a negative dielectric anisotropy, and arealigned vertical to the surface of the vertical alignment film, asillustrated in FIG. 1B, in the absence of an applied voltage across theliquid crystal layer 30 by virtue of a vertical alignment layer (notshown) which is provided on one surface of each of the TFT substrate 100a and the counter substrate 100 b that is closer to the liquid crystallayer 30. This state is described as the liquid crystal layer 30 beingin a vertical alignment. Note, however, that the liquid crystalmolecules 30 a of the liquid crystal layer 30 in a vertical alignmentmay slightly incline from the normal to the surface of the verticalalignment film (the surface of the substrate) depending upon the type ofvertical alignment film or the type of liquid crystal material used.Generally, a vertical alignment is defined as a state where the axis ofthe liquid crystal molecules (referred to also as the “axialorientation”) is oriented at an angle of about 85° or more with respectto the surface of the vertical alignment film.

[0137] The TFT substrate 100 a of the liquid crystal display device 100includes a transparent substrate (e.g., a glass substrate) 11 and apicture element electrode 14 provided on the surface of the transparentsubstrate 11. The counter substrate 100 b includes a transparentsubstrate (e.g., a glass substrate) 21 and a counter electrode 22provided on the surface of the transparent substrate 21. The orientationof the liquid crystal layer 30 changes for each picture element regionaccording to the voltage applied between the picture element electrode14 and the counter electrode 22 which are arranged so as to oppose eachother via the liquid crystal layer 30. A display is produced byutilizing a phenomenon that the polarization or amount of light passingthrough the liquid crystal layer 30 changes along with the change in theorientation of the liquid crystal layer 30.

[0138] The picture element electrode 14 of the liquid crystal displaydevice 100 includes a plurality of openings 14 a and a solid portion 14b. The opening 14 a refers to a portion of the picture element electrode14 made of a conductive film (e.g., an ITO film) from which theconductive film has been removed, and the solid portion 14 b refers to aportion thereof where the conductive film is present (the portion otherthan the openings 14 a). While a plurality of openings 14 a are formedfor each picture element electrode, the solid portion 14 b is basicallymade of a single continuous conductive film.

[0139] The openings 14 a are arranged so that the respective centersthereof form a square lattice, and a unit solid portion 14 b′ (definedas a portion of the solid portion 14 b that is substantially surroundedby four openings 14 a whose respective centers are located at the fourlattice points that form one unit lattice) has a generally circularshape. Each opening 14 a has a generally star shape having fourquarter-arc-shaped sides (edges) with a four-fold rotation axis at thecenter among the four sides. In order to stabilize the orientationacross the entire picture element region, the unit lattices preferablyexist up to the periphery of the picture element electrode 14.Therefore, a peripheral portion of the picture element electrode 14 ispreferably patterned, as illustrated in the figure, into a shape thatcorresponds to a generally half piece of the opening 14 a (in aperipheral portion of the picture element electrode 14 along a sidethereof) or into a shape that corresponds to a generally quarter pieceof the opening 14 a (in a peripheral portion of the picture elementelectrode 14 at a corner thereof). The square shown in a solid line inFIG. 1A (a collection of the square lattices) represents a region (outershape) corresponding to a conventional picture element electrode whichis made of a single conductive layer.

[0140] The openings 14 a located in the central portion of the pictureelement region have generally the same shape and size. The unit solidportions 14 b′ located respectively in unit lattices formed by theopenings 14 a are generally circular in shape, and have generally thesame shape and size. Each unit solid portion 14 b′ is connected toadjacent unit solid portions 14 b′, thereby forming the solid portion 14b which substantially functions as a single conductive film.

[0141] When a voltage is applied between the picture element electrode14 having such a structure as described above and the counter electrode22, an inclined electric field is produced at the edge portion of eachopening 14 a, thereby producing a plurality of liquid crystal domainseach having a radially-inclined orientation. The liquid crystal domainis produced in each region corresponding to the opening 14 a and in eachregion corresponding to the unit solid portion 14 b′, in a unit lattice.

[0142] Although an arrangement having a plurality of openings 14 a ineach picture element region is illustrated herein, it is possible toform a plurality of liquid crystal domains in each picture elementregion only by providing one opening therein. For example, assuming asquare region divided by broken lines into four unit lattices in FIG. 1Aas one picture element electrode, the picture element electrode is madeup of a single opening 14 a and four unit solid portions 14 b′, aroundthe opening 14 a, but it forms five liquid crystal domains each taking aradially-inclined orientation in the presence of an applied voltage.

[0143] Furthermore, a plurality of liquid crystal domains can be formedin each picture element region without providing the opening 14 a. Forexample, assuming two adjacent unit lattices as one picture elementelectrode, the picture element electrode is made up of two unit solidportions 14 b′ and does not include the opening 14 a. However, such apicture element electrode forms two liquid crystal domains each taking aradially-inclined orientation in the presence of an applied voltage.Thus, as long as the picture element electrode has unit solid portionssuch that a plurality of liquid crystal domains each taking aradially-inclined orientation at least in the presence of an appliedvoltage (in other words, as long as the picture element electrode hassuch an outer shape), the continuity in the orientation of the liquidcrystal molecules in each picture element region can be obtained, andthe radially-inclined orientation of each liquid crystal domain formedcorresponding to the unit solid portion 14 b′ is stabilized.

[0144] Moreover, while the picture element electrode 14 having a squareshape is illustrated herein, the shape of the picture element electrode14 is not limited to this. A typical shape of the picture elementelectrode 14 can be approximated to a rectangular shape (including asquare and an oblong rectangle), whereby the openings 14 a can beregularly arranged therein in a square lattice pattern. Even when thepicture element electrode 14 has a shape other than a rectangular shape,the effects of the present invention can be obtained as long as theopenings 14 a are arranged in a regular manner (e.g., in a squarelattice pattern as illustrated herein) so that liquid crystal domainsare formed in all regions in the picture element region.

[0145] The mechanism by which liquid crystal domains are formed by aninclined electric field as described above will be described withreference to FIG. 2A and FIG. 2B. Each of FIG. 2A and FIG. 2Billustrates the liquid crystal layer 30 illustrated in FIG. 1B with avoltage being applied thereacross. FIG. 2A schematically illustrates astate where the orientation of the liquid crystal molecules 30 a hasjust started to change (initial ON state) according to the voltageapplied across the liquid crystal layer 30. FIG. 2B schematicallyillustrates a state where the orientation of the liquid crystalmolecules 30 a has changed and become steady according to the appliedvoltage. Curves EQ in FIG. 2A and FIG. 2B denote equipotential lines.

[0146] As illustrated in FIG. 1A, when the picture element electrode 14and the counter electrode 22 are at the same potential (a state where novoltage is applied across the liquid crystal layer 30), the liquidcrystal molecules 30 a in each picture element region are alignedvertical to the surfaces of the substrates 11 and 21.

[0147] When a voltage is applied across the liquid crystal layer 30, apotential gradient represented by the equipotential lines EQ shown inFIG. 2A (perpendicular to the electric force line) is produced. Theequipotential lines EQ are parallel to the surface of the solid portion14 b and the counter electrode 22 in the liquid crystal layer 30 locatedbetween the solid portion 14 b of the picture element electrode 14 andthe counter electrode 22, and drop in a region corresponding to theopening 14 a of the picture element electrode 14. An inclined electricfield represented by an inclined portion of the equipotential lines EQis produced in the liquid crystal layer 30 above an edge portion EG ofthe opening 14 a (the peripheral portion of and within the opening 14 aincluding the boundary thereof).

[0148] A torque acts upon the liquid crystal molecules 30 a having anegative dielectric anisotropy so as to direct the axial orientation ofthe liquid crystal molecules 30 a to be parallel to the equipotentiallines EQ (perpendicular to the electric force line). Therefore, theliquid crystal molecules 30 a above the right edge portion EG in FIG. 2Aincline (rotate) clockwise and the liquid crystal molecules 30 a abovethe left edge portion EG incline (rotate) counterclockwise as indicatedby arrows in FIG. 2A. As a result, the liquid crystal molecules 30 aabove the edge portions EG are oriented parallel to the correspondingportions of the equipotential lines EQ.

[0149] Referring to FIG. 3A to FIG. 3D, the change in the orientation ofthe liquid crystal molecules 30 a will now be described in greaterdetail.

[0150] When an electric field is produced in the liquid crystal layer30, a torque acts upon the liquid crystal molecules 30 a having anegative dielectric anisotropy so as to direct the axial orientationthereof to be parallel to an equipotential line EQ. As illustrated inFIG. 3A, when an electric field represented by an equipotential line EQperpendicular to the axial orientation of the liquid crystal molecule 30a is produced, either a torque urging the liquid crystal molecule 30 ato incline clockwise or a torque urging the liquid crystal molecule 30 ato incline counterclockwise occurs with the same probability. Therefore,the liquid crystal layer 30 between the pair of parallel plate-shapeelectrodes opposing each other has some liquid crystal molecules 30 athat are subject to a clockwise torque and some other liquid crystalmolecules 30 a that are subject to a counterclockwise torque. As aresult, the transition to the intended orientation according to thevoltage applied across the liquid crystal layer 30 may not proceedsmoothly.

[0151] When an electric field represented by a portion of theequipotential lines EQ inclined with respect to the axial orientation ofthe liquid crystal molecules 30 a (an inclined electric field) isproduced at the edge portion EG of the opening 14 a of the liquidcrystal display device 100 of the present invention, as illustrated inFIG. 2A, the liquid crystal molecules 30 a incline in whicheverdirection (the counterclockwise direction in the illustrated example)that requires less rotation for the liquid crystal molecules 30 a to beparallel to the equipotential line EQ, as illustrated in FIG. 3B. Theliquid crystal molecules 30 a in a region where an electric fieldrepresented by an equipotential line EQ perpendicular to the axialorientation of the liquid crystal molecules 30 a is produced incline inthe same direction as the liquid crystal molecules 30 a located on theinclined portion of the equipotential lines EQ so that the orientationthereof is continuous (in conformity) with the orientation of the liquidcrystal molecules 30 a located on the inclined portion of theequipotential lines EQ as illustrated in FIG. 3C. As illustrated in FIG.3D, when an electric field such that the equipotential line EQ forms acontinuous concave/convex pattern, the liquid crystal molecules 30 alocated on a flat portion of the equipotential line EQ are oriented soas to conform with the orientation direction defined by the liquidcrystal molecules 30 a located on adjacent inclined portions of theequipotential line EQ. The phrase “being located on an equipotentialline EQ” as used herein means “being located within an electric fieldthat is represented by the equipotential line EQ”.

[0152] The change in the orientation of the liquid crystal molecules 30a, starting from those that are located on the inclined portion of theequipotential lines EQ, proceeds as described above and reaches a steadystate, which is schematically illustrated in FIG. 2B. The liquid crystalmolecules 30 a located around the central portion of the opening 14 aare influenced substantially equally by the respective orientations ofthe liquid crystal molecules 30 a at the opposing edge portions EG ofthe opening 14 a, and therefore retain their orientation perpendicularto the equipotential lines EQ. The liquid crystal molecules 30 a awayfrom the center of the opening 14 a incline by the influence of theorientation of other liquid crystal molecules 30 a at the closer edgeportion EG, thereby forming an inclined orientation that is symmetricabout the center SA of the opening 14 a. The orientation as viewed in adirection perpendicular to the display plane of the liquid crystaldisplay device 100 (a direction perpendicular to the surfaces of thesubstrates 11 and 21) is a state where the liquid crystal molecules 30 ahave a radial axial orientation (not shown) about the center of theopening 14 a. In the present specification, such an orientation will bereferred to as a “radially-inclined orientation”. Moreover, a region ofthe liquid crystal layer that takes a radially-inclined orientationabout a single axis will be referred to as a “liquid crystal domain”.

[0153] A liquid crystal domain in which the liquid crystal molecules 30a take a radially-inclined orientation is formed also in a regioncorresponding to the unit solid portion 14 b′ substantially surroundedby the openings 14 a. The liquid crystal molecules 30 a in a regioncorresponding to the unit solid portion 14 b′ are influenced by theorientation of the liquid crystal molecules 30 a at each edge portion EGof the opening 14 a so as to take a radially-inclined orientation thatis symmetric about the center SA of the unit solid portion 14 b′(corresponding to the center of a unit lattice formed by the openings 14a).

[0154] The radially-inclined orientation in a liquid crystal domainformed in the unit solid portion 14 b′ and the radially-inclinedorientation formed in the opening 14 a are continuous with each other,and are both in conformity with the orientation of the liquid crystalmolecules 30 a at the edge portion EG of the opening 14 a. The liquidcrystal molecules 30 a in the liquid crystal domain formed in theopening 14 a are oriented in the shape of a cone that spreads upwardly(toward the substrate 100 b), and the liquid crystal molecules 30 a inthe liquid crystal domain formed in the unit solid portion 14 b′ areoriented in the shape of a cone that spreads downwardly (toward thesubstrate 100 a). As described above, the radially-inclined orientationin a liquid crystal domain formed in the opening 14 a and that in aliquid crystal domain formed in the unit solid portion 14 b′ arecontinuous with each other. Therefore, no disclination line (orientationdefect) is formed along the boundary therebetween, thereby preventing adecrease in the display quality due to occurrence of a disclinationline.

[0155] In order to improve the viewing angle dependence, which is adisplay quality of a liquid crystal display device, in all azimuthangles, the existence probabilities of the liquid crystal molecules 30 aoriented in various azimuth angle directions preferably have rotationalsymmetry, and more preferably have axial symmetry, in each pictureelement region. In other words, the liquid crystal domain formed acrossthe entire picture element region preferably has rotational symmetry,and more preferably has axial symmetry. Note, however, that rotationalsymmetry may not be necessary across the entire picture element region,but it may be sufficient that each picture element region in the liquidcrystal layer is formed as a collection of a plurality of groups ofliquid crystal domains that are arranged so that each group hasrotational symmetry (or axial symmetry) (e.g., a plurality of groups ofliquid crystal domains, wherein each group of liquid crystal domains arearranged in a square lattice pattern). Therefore, the arrangement of theopenings 14 a formed in a picture element region may not need to haverotational symmetry across the entire picture element region, but it maybe sufficient that the arrangement can be represented as a collection ofa plurality of groups of openings that are arranged so that each grouphas rotational symmetry (or axial symmetry) (e.g., a plurality of groupsof openings, wherein each group of openings are arranged in a squarelattice pattern). Of course, this similarly applies to the arrangementof the unit solid portions 14 b′ substantially surrounded by theopenings 14 a. Moreover, since the shape of each liquid crystal domainpreferably has rotational symmetry, and more preferably axial symmetry,the shape of each opening 14 a and each unit solid portion 14 b′preferably has rotational symmetry, and more preferably axial symmetry.

[0156] Note that a sufficient voltage may not be applied across theliquid crystal layer 30 around the central portion of the opening 14 a,whereby the liquid crystal layer 30 around the central portion of theopening 14 a does not contribute to the display. In other words, even ifthe radially-inclined orientation of the liquid crystal layer 30 aroundthe central portion of the opening 14 a is disturbed to some extent(e.g., even if the central axis is shifted from the center of theopening 14 a), the display quality may not be decreased. Therefore, itmay be sufficient that at least the liquid crystal domain formedcorresponding to a unit solid portion 14 b′ is arranged to haverotational symmetry, and more preferably axial symmetry.

[0157] As described above with reference to FIG. 2A and FIG. 2B, thepicture element electrode 14 of the liquid crystal display device 100 ofthe present invention includes a plurality of openings 14 a andproduces, in the liquid crystal layer 30 in the picture element region,an electric field represented by equipotential lines EQ having inclinedportions. The liquid crystal molecules 30 a having a negative dielectricanisotropy in the liquid crystal layer 30, which are in a verticalalignment in the absence of an applied voltage, change the orientationdirection thereof, with the change in the orientation of those liquidcrystal molecules 30 a located on the inclined portion of theequipotential lines EQ serving as a trigger. Thus, a liquid crystaldomain having a stable radially-inclined orientation is formed in theopening 14 a and in the solid portion 14 b. A display is produced by thechange in the orientation of the liquid crystal molecules in the liquidcrystal domain according to the voltage applied across the liquidcrystal layer.

[0158] The shape (as viewed in the substrate normal direction) andarrangement of the openings 14 a of the picture element electrode 14 ofthe liquid crystal display device 100 will be described.

[0159] The display characteristics of a liquid crystal display deviceexhibit an azimuth angle dependence due to the orientation (opticalanisotropy) of the liquid crystal molecules. In order to reduce theazimuth angle dependence of the display characteristics, it is preferredthat the liquid crystal molecules are oriented in all azimuth angleswith substantially the same probability. More preferably, the liquidcrystal molecules in each picture element region are oriented in allazimuth angles with substantially the same probability. Therefore, theopening 14 a preferably has a shape such that liquid crystal domains areformed in each picture element region so that the liquid crystalmolecules 30 a in the picture element region are oriented in all azimuthangles with substantially the same probability. More specifically, theshape of the opening 14 a preferably has rotational symmetry (morepreferably symmetry with at least a two-fold rotation axis) about asymmetry axis extending through the center of each opening (in thenormal direction). It is also preferred that the plurality of openings14 a are arranged so as to have rotational symmetry. Moreover, it ispreferred that the shape of the unit solid portion 14 b′ which issubstantially surrounded by these openings also has rotational symmetry.It is also preferred that the unit solid portions 14 b′ are arranged soas to have rotational symmetry.

[0160] However, it may not be necessary to arrange the openings 14 a orthe unit solid portions 14 b′ so as to have rotational symmetry acrossthe entire picture element region. The liquid crystal molecules can beoriented in all azimuth angles with substantially the same probabilityacross the entire picture element region when, for example, a squarelattice (having symmetry with a four-fold rotation axis) is used as theminimum unit, and the picture element region is formed by such squarelattices, as illustrated in FIG. 1A.

[0161] The orientation of the liquid crystal molecules 30 a when thegenerally star-shaped openings 14 a having rotational symmetry and thegenerally circular unit solid portions 14 b′, are arranged in a squarelattice pattern, as illustrated in FIG. 1A, will be described withreference to FIG. 4A to FIG. 4C.

[0162] Each of FIG. 4A to FIG. 4C schematically illustrates anorientation of the liquid crystal molecules 30 a as viewed in thesubstrate normal direction. In figures, such as FIG. 4B and FIG. 4C,illustrating the orientation of the liquid crystal molecules 30 a asviewed in the substrate normal direction, a black-spotted end of theliquid crystal molecule 30 a drawn as an ellipse indicates that theliquid crystal molecule 30 a is inclined so that the end is closer thanthe other end to the substrate on which the picture element electrode 14having the opening 14 a is provided. This similarly applies to all ofthe subsequent figures. A single unit lattice (which is formed by fouropenings 14 a) in the picture element region illustrated in FIG. 1A willbe described below. Cross-sectional views taken along the respectivediagonals of FIG. 4A to FIG. 4C correspond to FIG. 1B, FIG. 2A and FIG.2B, respectively, and FIG. 1B, FIG. 2A and FIG. 2B will also be referredto in the following description.

[0163] When the picture element electrode 14 and the counter electrode22 are at the same potential, i.e., in a state where no voltage isapplied across the liquid crystal layer 30, the liquid crystal molecules30 a whose orientation direction is regulated by the vertical alignmentlayer (not shown) which is provided on one side of each of the TFTsubstrate 100 a and the counter substrate 100 b that is closer to theliquid crystal layer 30 take a vertical alignment as illustrated in FIG.4A.

[0164] When an electric field is applied across the liquid crystal layer30 so as to produce an electric field represented by equipotential linesEQ shown in FIG. 2A, a torque acts upon the liquid crystal molecules 30a having a negative dielectric anisotropy so as to direct the axialorientation thereof to be parallel to the equipotential lines EQ. Asdescribed above with reference to FIG. 3A and FIG. 3B, for the liquidcrystal molecules 30 a under an electric field represented byequipotential lines EQ perpendicular to the molecular axis thereof, thedirection in which the liquid crystal molecules 30 a are to incline(rotate) is not uniquely defined (FIG. 3A), whereby the orientationchange (inclination or rotation) does not easily occur. In contrast, forthe liquid crystal molecules 30 a placed under equipotential lines EQinclined with respect to the molecular axis of the liquid crystalmolecules 30 a, the direction of inclination (rotation) is uniquelydefined, whereby the orientation change easily occurs. Therefore, asillustrated in FIG. 4B, the liquid crystal molecules 30 a startinclining from the edge portion of the opening 14 a where the molecularaxis of the liquid crystal molecules 30 a is inclined with respect tothe equipotential lines EQ. Then, the surrounding liquid crystalmolecules 30 a incline so as to conform with the orientation of thealready-inclined liquid crystal molecules 30 a at the edge portion ofthe opening 14 a, as described above with reference to FIG. 3C. Then,the axial orientation of the liquid crystal molecules 30 a becomesstable as illustrated in FIG. 4C (radially-inclined orientation).

[0165] As described above, when the shape of the opening 14 a hasrotational symmetry, the liquid crystal molecules 30 a in the pictureelement region successively incline, starting from the edge portion ofthe opening 14 a toward the center of the opening 14 a upon applicationof a voltage. As a result, there is obtained an orientation in whichthose liquid crystal molecules 30 a around the center of the opening 14a, where the respective orientation-regulating forces from the liquidcrystal molecules 30 a at the edge portions are in equilibrium, remainin a vertical alignment with respect to the substrate plane, while thesurrounding liquid crystal molecules 30 a are inclined in a radialpattern about those liquid crystal molecules 30 a around the center ofthe opening 14 a, with the degree of inclination gradually increasingaway from the center of the opening 14 a.

[0166] The liquid crystal molecules 30 a in a region corresponding tothe generally circular unit solid portion 14 b′, which is surrounded bythe four generally star-shaped openings 14 a arranged in a squarelattice pattern also incline so as to conform with the orientation ofthe liquid crystal molecules 30 a which have been inclined by aninclined electric field produced at the edge portion of each opening 14a. As a result, there is obtained an orientation in which those liquidcrystal molecules 30 a around the center of the unit solid portion 14b′, where the respective orientation-regulating forces from the liquidcrystal molecules 30 a at the edge portions are in equilibrium, remainin a vertical alignment with respect to the substrate plane, while thesurrounding liquid crystal molecules 30 a are inclined in a radialpattern about those liquid crystal molecules 30 a around the center ofthe unit solid portion 14 b′, with the degree of inclination graduallyincreasing away from the center of the unit solid portion 14 b′.

[0167] As described above, when liquid crystal domains in each of whichthe liquid crystal molecules 30 a take a radially-inclined orientationare arranged in a square lattice pattern across the entire pictureelement region, the existence probabilities of the liquid crystalmolecules 30 a of the respective axial orientations have rotationalsymmetry, whereby it is possible to realize a high-quality displaywithout non-uniformity for any viewing angle. In order to reduce theviewing angle dependence of a liquid crystal domain having aradially-inclined orientation, the liquid crystal domain preferably hasa high degree of rotational symmetry (preferably with at least atwo-fold rotation axis, and more preferably with at least a four-foldrotation axis). Moreover, in order to reduce the viewing angledependence across the entire picture element region, the plurality ofliquid crystal domains provided in the picture element region arepreferably arranged in a pattern (e.g., a square lattice pattern) thatis a combination of a plurality of unit patterns (e.g., unit latticepatterns) each having a high degree of rotational symmetry (preferablywith at least a two-fold rotation axis, and more preferably with atleast a four-fold rotation axis).

[0168] For the radially-inclined orientation of the liquid crystalmolecules 30 a, a radially-inclined orientation having acounterclockwise or clockwise spiral pattern as illustrated in FIG. 5Bor FIG. 5C, respectively, is more stable than the simpleradially-inclined orientation as illustrated in FIG. 5A. The spiralorientation is different from a normal twist orientation (in which theorientation direction of the liquid crystal molecules 30 a spirallychanges along the thickness of the liquid crystal layer 30). In thespiral orientation, the orientation direction of the liquid crystalmolecules 30 a does not substantially change along the thickness of theliquid crystal layer 30 for a minute region. In other words, theorientation in a cross section (in a plane parallel to the layer plane)at any thickness of the liquid crystal layer 30 is as illustrated inFIG. 5B or FIG. 5C, with substantially no twist deformation along thethickness of the liquid crystal layer 30. For a liquid crystal domain asa whole, however, there may be a certain degree of twist deformation.

[0169] When a material obtained by adding a chiral agent to a nematicliquid crystal material having a negative dielectric anisotropy is used,the liquid crystal molecules 30 a take a radially-inclined orientationof a counterclockwise or clockwise spiral pattern about the opening 14 aand the unit solid portion 14 b′, as illustrated in FIG. 5B or FIG. 5C,respectively, in the presence of an applied voltage. Whether the spiralpattern is counterclockwise or clockwise is determined by the type ofchiral agent used. Thus, by controlling the liquid crystal layer 30 inthe opening 14 a into a radially-inclined orientation of a spiralpattern in the presence of an applied voltage, the direction of thespiral pattern of the radially-inclined liquid crystal molecules 30 aabout other liquid crystal molecules 30 a standing vertical to thesubstrate plane can be constant in all liquid crystal domains, wherebyit is possible to realize a uniform display without displaynon-uniformity. Since the direction of the spiral pattern around theliquid crystal molecules 30 a standing vertical to the substrate planeis definite, the response speed upon application of a voltage across theliquid crystal layer 30 is also improved.

[0170] Moreover, when a chiral agent is added, the orientation of theliquid crystal molecules 30 a changes in a spiral pattern along thethickness of the liquid crystal layer 30 as in a normal twistorientation. In an orientation where the orientation of the liquidcrystal molecules 30 a does not change in a spiral pattern along thethickness of the liquid crystal layer 30, the liquid crystal molecules30 a which are oriented perpendicular or parallel to the polarizationaxis of the polarization plate do not give a phase difference to theincident light, whereby incident light passing through a region of suchan orientation does not contribute to the transmittance. In contrast, inan orientation where the orientation of the liquid crystal molecules 30a changes in a spiral pattern along the thickness of the liquid crystallayer 30, the liquid crystal molecules 30 a that are orientedperpendicular or parallel to the polarization axis of the polarizationplate also give a phase difference to the incident light, and theoptical rotatory power can also be utilized, whereby incident lightpassing through a region of such an orientation also contributes to thetransmittance. Thus, it is possible to obtain a liquid crystal displaydevice capable of producing a bright display.

[0171]FIG. 1A illustrates an example in which each opening 14 a has agenerally star shape and each unit solid portion 14 b′ has a generallycircular shape, wherein such openings 14 a and such unit solid portions14 b′ are arranged in a square lattice pattern. However, the shape ofthe opening 14 a, the shape of the unit solid portion 14 b′, and thearrangement thereof are not limited to those of the example above.

[0172]FIG. 6A and FIG. 6B are plan views respectively illustratingpicture element electrodes 14A and 14B having respective openings 14 aand unit solid portions 14 b′ of different shapes.

[0173] The openings 14 a and the unit solid portions 14 b′ of thepicture element electrodes 14A and 14B illustrated in FIG. 6A and FIG.6B, respectively, are slightly distorted from those of the pictureelement electrode illustrated in FIG. 1A. The openings 14 a and the unitsolid portions 14 b′ of the picture element electrodes 14A and 14B havea two-fold rotation axis (not a four-fold rotation axis) and areregularly arranged so as to form oblong rectangular unit lattices. Inboth of the picture element electrodes 14A and 14B, the opening 14 a hasa distorted star shape, and the unit solid portion 14 b′ has a generallyelliptical shape (a distorted circular shape). Also with the pictureelement electrodes 14A and 14B, it is possible to obtain a liquidcrystal display device having a high display quality and a desirableviewing angle characteristic.

[0174] Moreover, picture element electrodes 14C and 14D as illustratedin FIG. 7A and FIG. 7B, respectively, may alternatively be used.

[0175] In the picture element electrodes 14C and 14D, generallycross-shaped openings 14 a are arranged in a square lattice pattern sothat each unit solid portion 14 b′ has a generally square shape. Ofcourse, the patterns of the picture element electrodes 14C and 14D maybe distorted so that there are oblong rectangular unit lattices. Asdescribed above, it is possible to obtain a liquid crystal displaydevice having a high display quality and a desirable viewing anglecharacteristic alternatively by regularly arranging the generallyrectangular (including a square and oblong rectangle) unit solidportions 14 b′.

[0176] However, the shape of the opening 14 a and/or the unit solidportion 14 b′, is preferably a circle or an ellipse, rather than arectangle, so that a radially-inclined orientation is more stable. It isbelieved that a radially-inclined orientation is more stable with acircular or elliptical opening and/or unit solid portion because theedge of the opening 14 a is more continuous (smooth), whereby theorientation direction of the liquid crystal molecules 30 a changes morecontinuously (smoothly).

[0177] In view of the continuity of the orientation direction of theliquid crystal molecules 30 a described above, picture elementelectrodes 14E and 14F as illustrated in FIG. 8A and FIG. 8B,respectively, are also desirable. The picture element electrode 14Eillustrated in FIG. 8A is a variation of the picture element electrode14 illustrated in FIG. 1A in which each opening 14 a is simply comprisedof four arcs. The picture element electrode 14F illustrated in FIG. 8Bis a variation of the picture element electrode 14D illustrated in FIG.7B in which each side of the opening 14 a on the unit solid portion 14b′ is an arc. In both of the picture element electrodes 14E and 14F, theopenings 14 a and the unit solid portions 14 b′ have a four-foldrotation axis and are arranged in a square lattice pattern (having afour-fold rotation axis). Alternatively, the shape of the unit solidportion 14 b′, of the opening 14 a may be distorted into a shape havinga two-fold rotation axis, and such unit solid portions 14 b′ may bearranged so as to form oblong rectangular lattices (having a two-foldrotation axis), as illustrated in FIG. 6A and FIG. 6B.

[0178] In view of the response speed, picture element electrodes 14G and14H as illustrated in FIG. 9A and FIG. 9B, respectively, may be used.The picture element electrode 14G illustrated in FIG. 9A is a variationof the picture element electrode 14C having the generally square unitsolid portion 14 b′, illustrated in FIG. 7A in which the shape of theunit solid portion 14 b′ of the picture element electrode 14G is adistorted square shape having acute angle corners. Moreover, the shapeof the unit solid portion 14 b′ of the picture element electrode 14Hillustrated in FIG. 9B is a generally star shape having eight edges andhaving a four-fold rotation axis at its center with each corner havingan acute angle. Note that a corner with an acute angle as used hereinrefers to a corner or a rounded corner having an angle less than 90°.

[0179] When a voltage is applied across the liquid crystal layer 30 in aliquid crystal display device in which the orientation of the liquidcrystal molecules 30 a is controlled by an inclined electric fieldproduced at an edge portion of the opening 14 a, the liquid crystalmolecules 30 a above an edge portion incline first, followed by thesurrounding liquid crystal molecules 30 a, eventually resulting in aradially-inclined orientation. Therefore, the response speed may belower than that of a liquid crystal display device of a display mode inwhich liquid crystal molecules on a picture element electrode incline atonce upon application of a voltage across the liquid crystal layer.

[0180] When the unit solid portion 14 b′ has a shape with acute anglecorners as illustrated in FIG. 9A and FIG. 9B, the total amount orlength of the edge portion that produces an inclined electric field isincreased, whereby the inclined electric field can act upon more liquidcrystal molecules 30 a. Therefore, the number of liquid crystalmolecules 30 a that initially start inclining in response to an appliedelectric field increases, thereby reducing the amount of time requiredto achieve the radially-inclined orientation across the entire pictureelement region, and thus improving the response speed to the applicationof a voltage across the liquid crystal layer 30.

[0181] For example, for a liquid crystal display device in which eachside of the unit solid portion 14 b′ has a length of about 40 μm, theresponse speed to the application of a voltage across the liquid crystallayer 30 can be reduced by about 60% in a case where the shape of theunit solid portion 14 b′ is a distorted square shape as illustrated inFIG. 9A and the angle ea between two edges forming a corner is less than90° as illustrated in FIG. 10A, than in a case where the shape of theunit solid portion 14 b′ is a generally square shape as illustrated inFIG. 8B and the angle θa between two edges forming a corner is 90° asillustrated in FIG. 10B. Of course, the response speed can similarly bereduced when a generally star shape as illustrated in FIG. 9B isemployed for the shape of the unit solid portion 14 b′.

[0182] Moreover, when the unit solid portion 14 b′ has a shape withacute angle corners, the existence probability of the liquid crystalmolecules 30 a that are oriented in a particular azimuth angle directioncan be increased (or decreased) as compared to a case where the shape ofthe unit solid portion 14 b′ is a generally circular shape or agenerally rectangular shape. In other words, a high directionality canbe introduced in the existence probabilities of the liquid crystalmolecules 30 a oriented in various azimuth angle directions. Therefore,when an acute angle corner is employed in the unit solid portion 14 b′,in a liquid crystal display device having a polarization plate in whichlinearly-polarized light is incident upon the liquid crystal layer 30,it is possible to decrease the existence probability of the liquidcrystal molecules 30 a oriented vertical or horizontal to thepolarization axis of the polarization plate, i.e., the liquid crystalmolecules 30 a that do not give a phase difference to the incidentlight. Thus, it is possible to improve the light transmittance and torealize a brighter display.

[0183]FIG. 11A illustrates a change in the transmittance as the angle ofthe polarization axis of the polarization plate is changed in a liquidcrystal display device with the picture element electrode 14Fillustrated in FIG. 8B having the unit solid portion 14 b′, of agenerally square shape and in a liquid crystal display device with thepicture element electrode 14H illustrated in FIG. 9B having the unitsolid portion 14 b′ of a generally star shape. In FIG. 11A, a solid line51 represents the transmittance of the liquid crystal display devicewith the picture element electrode 14F illustrated in FIG. 8B in thepresence of an applied voltage, and a broken line 52 represents thetransmittance of the liquid crystal display device with the pictureelement electrode 14H illustrated in FIG. 9B in the presence of anapplied voltage. Note that in FIG. 11A, the angle being 0° correspondsto a state where the polarization axis of the polarization plate on theviewer side (represented by a solid line arrow 61) extends in thetop-bottom direction of the display plane (corresponding to thetop-bottom direction of the figure) while the polarization axis of thepolarization plate on the reverse side (represented by a broken linearrow 62) extends in the left-right direction of the display plane(corresponding to the left-right direction of the figure), asillustrated in FIG. 11B, with an angle of a positive value and anegative value indicating an angle obtained by rotating the polarizationaxis counterclockwise and clockwise, respectively.

[0184] As illustrated in FIG. 11A, the maximum value of thetransmittance of the liquid crystal display device having the pictureelement electrode 14H in which the unit solid portion 14 b′ has acuteangle corners (the broken line 52) is greater than the maximum value ofthe transmittance of the liquid crystal display device having thepicture element electrode 14F in which the unit solid portion 14 b′ hasa generally square shape (the solid line 51). Thus, by employing acuteangle corners in the unit solid portion 14 b′, it is possible to improvethe transmittance and to produce a brighter display.

[0185] Note that when the unit solid portion 14 b′, has acute anglecorners as described above, the response speed and the transmittance canbe improved, but the stability of the radially-inclined orientation maydeteriorate. Where acute angle corners are employed, as compared to acase where the shape of the unit solid portion 14 b′ is a generallycircular shape, for example, the edge of the opening 14 a is not assmooth as that in the case where the shape of the unit solid portion 14b′ is a generally circular shape, thereby resulting in a poor continuityin the change of the orientation direction of the liquid crystalmolecules 30 a. Thus, the stability of the radially-inclined orientationmay deteriorate. However, a practically sufficient orientation stabilitycan be obtained if a second orientation-regulating structure to bedescribed later is employed in combination.

[0186] While examples where a plurality of openings 14 a are provided inone picture element region have been illustrated in FIG. 6A to FIG. 9B,a plurality of liquid crystal domains can be formed in one pictureelement region by providing only one opening as described above withreference to FIG. 1A and FIG. 1B. Furthermore, a plurality of liquidcrystal domains can be formed in each picture element region even whenno opening 14 a is formed. Moreover, it may not be necessary to form aliquid crystal domain that takes a radially-inclined orientation in aregion corresponding to the opening 14 a of the picture elementelectrode. As long as a liquid crystal domain taking a radially-inclinedorientation is formed so as to correspond to the solid portion 14 b (theunit solid portion 14 b′), a continuity of the orientation of the liquidcrystal molecules in each picture element region is ensured, therebystabilizing the radially-inclined orientation of the liquid crystaldomain formed so as to correspond to the solid portion 14 b, even when aliquid crystal domain formed so as to correspond to the opening 14 adoes not take a radially-inclined orientation. Particularly, when thearea of the opening 14 a is small, as illustrated in FIG. 7A and FIG.7B, the opening has only a little contribution to the display, and thusthe display quality will not deteriorate significantly even if a liquidcrystal domain taking a radially-inclined orientation is not formed in aregion corresponding to the opening.

[0187] In the examples described above, the openings 14 a are generallystar-shaped or generally cross-shaped, and the unit solid portions 14b′, are generally circular, generally elliptical, generally square(rectangular), and generally rectangular with rounded corners.Alternatively, the negative-positive relationship between the openings14 a and the unit solid portions 14 b′ may be inverted (hereinafter, theinversion of the negative-positive relationship between the openings 14a and the unit solid portions 14 b′ will be referred to simply as“inversion”). For example, FIG. 12 illustrates a picture elementelectrode 14I having a pattern obtained by inverting thenegative-positive relationship between the openings 14 a and the unitsolid portions 14 b′, of the picture element electrode 14 illustrated inFIG. 1A. The picture element electrode 14I having an inverted patternhas substantially the same function as that of the picture elementelectrode 14 illustrated in FIG. 1A. When the opening 14 a and the unitsolid portion 14 b′ both have a generally square shape, as in pictureelement electrodes 14J and 14K illustrated in FIG. 13A and FIG. 13B,respectively, the inverted pattern may be substantially the same as theoriginal pattern.

[0188] Also when the pattern illustrated in FIG. 1A is inverted as inthe pattern illustrated in FIG. 12, it is preferred to form partialpieces (generally half or quarter pieces) of the opening 14 a so as toform the unit solid portions 14 b′, having rotational symmetry at theedge portion of the picture element electrode 14. By employing such apattern, the effect of an inclined electric field can be obtained at theedge portion of a picture element region as in the central portion ofthe picture element region, whereby it is possible to realize a stableradially-inclined orientation across the entire picture element region.

[0189] Next, which one of two inverted patterns should be employed willbe discussed with respect to the picture element electrode 14 of FIG. 1Aand the picture element electrode 14I illustrated in FIG. 12 having apattern obtained by inverting the pattern of the openings 14 a and theunit solid portions 14 b′ of the picture element electrode 14.

[0190] With either pattern, the length of the perimeter of each opening14 a is the same. Therefore, for the function of producing an inclinedelectric field, there is no difference between the two patterns.However, the area ratio of the unit solid portion 14 b′ (with respect tothe total area of the picture element electrode 14) may differ betweenthe two patterns. In other words, the area of the solid portion 14 b(the portion where the conductive film exists) for producing an electricfield acting upon the liquid crystal molecules of the liquid crystallayer may differ therebetween.

[0191] The voltage applied through a liquid crystal domain formed in theopening 14 a is lower than the voltage applied through another liquidcrystal domain formed in the solid portion 14 b. As a result, in anormally black mode display, for example, the liquid crystal domainformed in the opening 14 a appears darker. Thus, as the area ratio ofthe openings 14 a increases, the display brightness decreases.Therefore, it is preferred that the area ratio of the solid portion 14 bis high.

[0192] Whether the area ratio of the solid portion 14 b is higher in thepattern of FIG. 1A or in the pattern of FIG. 12 depends upon the pitch(size) of the unit lattice.

[0193]FIG. 14A illustrates a unit lattice of the pattern illustrated inFIG. 1A, and FIG. 14B illustrates a unit lattice of the patternillustrated in FIG. 12 (the opening 14 a being taken as the center ofeach lattice). The portions illustrated in FIG. 12 that serve to connectadjacent unit solid portions 14 b′ together (the branch portionsextending in four directions from the circular portion) are omitted inFIG. 14B. The length of one side of the square unit lattice (the pitch)is denoted by “p”, and the distance between the opening 14 a or the unitsolid portion 14 b′ and a side of the unit lattice (the width of theside space) is denoted by “s”.

[0194] Various samples of picture element electrodes 14 having differentpitches p and side spaces s were produced so as to examine the stabilityof the radially-inclined orientation, etc. As a result, it was foundthat with the picture element electrode 14 having a pattern illustratedin FIG. 14A (hereinafter, referred to as the “positive pattern”), theside space s needs to be about 2.75 μm or more so as to produce aninclined electric field required to obtain a radially-inclinedorientation. It was found that with the picture element electrode 14having a pattern illustrated in FIG. 14B (hereinafter, referred to asthe “negative pattern”), the side space s needs to be about 2.25 μm ormore so as to produce an inclined electric field required to obtain aradially-inclined orientation. For each pattern, the area ratio of thesolid portion 14 b was examined while changing the value of the pitch pwith the side space s fixed to its lower limit value above. The resultsare shown in Table 1 below and in FIG. 14C. TABLE 1 Solid portion arearatio (%) Pitch p (μm) Positive (FIG. 14A) Negative (FIG. 14B) 20 41.352.9 25 47.8 47.2 30 52.4 43.3 35 55.8 40.4 40 58.4 38.2 45 60.5 36.4 5062.2 35.0

[0195] As can be seen from Table 1 and FIG. 14C, the positive pattern(FIG. 14A) has a higher area ratio of the solid portion 14 b when thepitch p is about 25 μm or more, and the negative pattern (FIG. 14B) hasa higher area ratio of the solid portion 14 b when the pitch p is lessthan about 25 μm. Therefore, in view of the display brightness and thestability of orientation, the pattern which should be employed changesat the critical pitch p of about 25 μm. For example, when three or fewerunit lattices are provided in the width direction of the picture elementelectrode 14 having a width of 75 μm, the positive pattern illustratedin FIG. 14A is preferred, and when four or more unit lattices areprovided, the negative pattern illustrated in FIG. 14B is preferred. Forpatterns other than that illustrated herein, the selection between apositive pattern and a negative pattern can similarly be made so as toobtain the larger area ratio of the solid portion 14 b.

[0196] The number of unit lattices can be determined as follows. Thesize of each unit lattice is calculated so that one or more (an integernumber of) unit lattices are arranged along the width (horizontal orvertical) of the picture element electrode 14, and the area ratio of thesolid portion is calculated for each calculated unit lattice size. Then,the unit lattice size such that the area ratio of the solid portion ismaximized is selected. Note that the orientation-regulating force froman inclined electric field decreases, whereby a stable radially-inclinedorientation is not easily obtained, when the diameter of the unit solidportion 14 b′, (for the positive pattern) or the opening 14 a (for thenegative pattern) is less than 15 μm. The lower limit diameter value isfor a case where the thickness of the liquid crystal layer 30 is about 3μm. When the thickness of the liquid crystal layer 30 is less than about3 μm, a stable radially-inclined orientation can be obtained even whenthe diameter of the unit solid portion 14 b′ and the opening 14 a isless than the lower limit value. When the thickness of the liquidcrystal layer 30 is greater than about 3 μm, the lower limit diametervalue of the unit solid portion 14 b′ and the opening 14 a for obtaininga stable radially-inclined orientation is greater than the lower limitvalue shown above.

[0197] Note that the stability of the radially-inclined orientation canbe increased by forming a protrusion in the opening 14 a as will bedescribed later. The conditions shown above are all given for caseswhere the protrusion is not formed.

[0198] Except that the picture element electrode 14 is an electrodehaving the openings 14 a, the liquid crystal display device 100described above may employ the same structure as that of a knownvertical alignment type liquid crystal display device and can beproduced by a known production method.

[0199] Typically, a vertical alignment layer (not shown) is provided onone side of each of the picture element electrode 14 and the counterelectrode 22 that is closer to the liquid crystal layer 30 so as tovertically align the liquid crystal molecules having a negativedielectric anisotropy.

[0200] The liquid crystal material may be a nematic liquid crystalmaterial having a negative dielectric anisotropy. A guest-host modeliquid crystal display device can be obtained by adding a dichroic dyeto a nematic liquid crystal material having a negative dielectricanisotropy. A guest-host mode liquid crystal display device does notrequire a polarization plate.

[0201] A structure of one picture element region of another liquidcrystal display device 200 having the first orientation-regulatingstructure of the present invention will be described with reference toFIG. 15A and FIG. 15B. In the subsequent figures, each element havingsubstantially the same function as that of the liquid crystal displaydevice 100 will be denoted by the same reference numeral and will not befurther described. FIG. 15A is a plan view as viewed in the substratenormal direction, and FIG. 15B is a cross-sectional view taken alongline 15B-15B′ of FIG. 15A. FIG. 15B illustrates a state where no voltageis applied across the liquid crystal layer.

[0202] As illustrated in FIG. 15A and FIG. 15B, the liquid crystaldisplay device 200 is different from the liquid crystal display device100 illustrated in FIG. 1A and FIG. 1B in that a TFT substrate 200 aincludes a protrusion 40 in the opening 14 a of the picture elementelectrode 14. A vertical alignment film (not shown) is provided on thesurface of the protrusion 40.

[0203] The cross section of the protrusion 40 along the plane of thesubstrate 11 is a generally star-shaped cross section, i.e., the sameshape as that of the opening 14 a, as illustrated in FIG. 15A. Note thatadjacent protrusions 40 are connected to each other so as to completelysurround each unit solid portion 14 b′ in a generally circular pattern.The cross section of the protrusion 40 along a plane vertical to thesubstrate 11 is a trapezoidal shape as illustrated in FIG. 15B.Specifically, the cross section has a top surface 40 t parallel to thesubstrate plane and a side surface 40 s inclined by a taper angle θ(<90°) with respect to the substrate plane. Since the vertical alignmentfilm (not shown) is provided so as to cover the protrusion 40, the sidesurface 40s of the protrusion 40 has an orientation-regulating force ofthe same direction as that of an inclined electric field for the liquidcrystal molecules 30 a of the liquid crystal layer 30, therebyfunctioning to stabilize the radially-inclined orientation.

[0204] The function of the protrusion 40 will now be described withreference to FIG. 16A to FIG. 16D, FIG. 17A and FIG. 17B.

[0205] First, the relationship between the orientation of the liquidcrystal molecules 30 a and the configuration of the surface having avertical alignment power will be described with reference to FIG. 16A toFIG. 16D.

[0206] As illustrated in FIG. 16A, a liquid crystal molecule 30 a on ahorizontal surface is aligned vertical to the surface due to theorientation-regulating force of the surface having a vertical alignmentpower (typically, the surface of a vertical alignment film). When anelectric field represented by an equipotential line EQ perpendicular tothe axial orientation of the liquid crystal molecule 30 a is appliedthrough the liquid crystal molecule 30 a in a vertical alignment, atorque urging the liquid crystal molecule 30 a to incline clockwise anda torque urging the liquid crystal molecule 30 a to inclinecounterclockwise act upon the liquid crystal molecule 30 a with the sameprobability. Therefore, in the liquid crystal layer 30 between a pair ofopposing electrodes in a parallel plate arrangement include some liquidcrystal molecules 30 a that are subject to the clockwise torque andother liquid crystal molecules 30 a that are subject to thecounterclockwise torque. As a result, the transition to the orientationaccording to the voltage applied across the liquid crystal layer 30 maynot proceed smoothly.

[0207] When an electric field represented by a horizontal equipotentialline EQ is applied through a liquid crystal molecule 30 a verticallyaligned to an inclined surface, as illustrated in FIG. 16B, the liquidcrystal molecule 30 a inclines in whichever direction (the clockwisedirection in the illustrated example) that requires less inclination forthe liquid crystal molecule 30 a to be parallel to the equipotentialline EQ. Then, as illustrated in FIG. 16C, other adjacent liquid crystalmolecules 30 a aligned vertical to a horizontal surface incline in thesame direction (the clockwise direction) as the liquid crystal molecule30 a located on the inclined surface so that the orientation thereof iscontinuous (in conformity) with the orientation of the liquid crystalmolecule 30 a aligned vertical to the inclined surface.

[0208] As illustrated in FIG. 16D, for a surface with concave/convexportions whose cross section includes a series of trapezoids, the liquidcrystal molecules 30 a on the top surface and those on the bottomsurface are oriented so as to conform with the orientation directionregulated by other liquid crystal molecules 30 a on the inclinedportions of the surface.

[0209] In the liquid crystal display device 200, the direction of theorientation-regulating force exerted by the configuration (protrusions)of the surface is aligned with the direction of theorientation-regulating force exerted by an inclined electric field,thereby stabilizing the radially-inclined orientation.

[0210]FIG. 17A and FIG. 17B each illustrate a state in the presence ofan applied voltage across the liquid crystal layer 30 shown in FIG. 15B.FIG. 17A schematically illustrates a state where the orientation of theliquid crystal molecules 30 a has just started to change (initial ONstate) according to the voltage applied across the liquid crystal layer30. FIG. 17B schematically illustrates a state where the orientation ofthe liquid crystal molecules 30 a has changed and become steadyaccording to the applied voltage. In FIG. 17A and FIG. 17B, curves EQdenote equipotential lines.

[0211] When the picture element electrode 14 and the counter electrode22 are at the same potential (i.e., in a state where no voltage isapplied across the liquid crystal layer 30), the liquid crystalmolecules 30 a in each picture element region are aligned vertical tothe surfaces of the substrates 11 and 21 as illustrated in FIG. 15B. Theliquid crystal molecules 30 a in contact with the vertical alignmentfilm (not shown) on the side surface 40 s of the protrusion 40 arealigned vertical to the side surface 40 s, and the liquid crystalmolecules 30 a in the vicinity of the side surface 40 s take an inclinedorientation as illustrated due to the interaction (the nature as anelastic continuum) with the surrounding liquid crystal molecules 30 a.

[0212] When a voltage is applied across the liquid crystal layer 30, apotential gradient represented by equipotential lines EQ shown in FIG.17A is produced. The equipotential lines EQ are parallel to the surfacesof the solid portion 14 b and the counter electrode 22 in a region ofthe liquid crystal layer 30 located between the solid portion 14 b ofthe picture element electrode 14 and the counter electrode 22, and dropin a region corresponding to the opening 14 a of the picture elementelectrode 14, thereby producing an inclined electric field representedby the inclined portion of the equipotential lines EQ in each region ofthe liquid crystal layer 30 above an edge portion (the peripheralportion of and within the opening 14 a including the boundary thereof)EG of the opening 14 a.

[0213] Due to the inclined electric field, the liquid crystal molecules30 a above the right edge portion EG in FIG. 17A incline (rotate)clockwise and the liquid crystal molecules 30 a above the left edgeportion EG incline (rotate) counterclockwise as indicated by arrows inFIG. 17A, as described above, so as to be parallel to the equipotentiallines EQ. The direction of the orientation-regulating force exerted bythe inclined electric field is the same as that of theorientation-regulating force exerted by the side surface 40 s located ateach edge portion EG.

[0214] As described above, the change in the orientation starts from theliquid crystal molecules 30 a located on the inclined portion of theequipotential lines EQ, and reaches a steady state of the orientationschematically illustrated in FIG. 17B. The liquid crystal molecules 30 aaround the central portion of the opening 14 a, i.e., around the centralportion of the top surface 40 t of the protrusion 40, are substantiallyequally influenced by the respective orientations of the liquid crystalmolecules 30 a at the opposing edge portions EG of the opening 14 a, andtherefore retain their orientation perpendicular to the equipotentiallines EQ. The liquid crystal molecules 30 a away from the center of theopening 14 a (the top surface 40 t of the protrusion 40) incline by theinfluence of the orientation of other liquid crystal molecules 30 a atthe closer edge portion EG, thereby forming an inclined orientation thatis symmetric about the center SA of the opening 14 a (the top surface 40t of the protrusion 40). An inclined orientation symmetric about thecenter SA of the unit solid portion 14 b′ is formed also in the regioncorresponding to the unit solid portion 14 b′, which is substantiallysurrounded by the openings 14 a and the protrusions 40.

[0215] As described above, in the liquid crystal display device 200, asin the liquid crystal display device 100, liquid crystal domains eachhaving a radially-inclined orientation are formed corresponding to theopenings 14 a and the unit solid portions 14 b′. Since the protrusions40 are provided so as to completely surround each unit solid portion 14b′, in a generally circular pattern, each liquid crystal domain isformed corresponding to the generally circular region surrounded by theprotrusions 40. Moreover, the side surface of the protrusion 40 providedin the opening 14 a functions to incline the liquid crystal molecules 30a in the vicinity of the edge portion EG of the opening 14 a in the samedirection as the direction of the orientation-regulating force exertedby the inclined electric field, thereby stabilizing theradially-inclined orientation.

[0216] Of course, the orientation-regulating force exerted by theinclined electric field only acts in the presence of an applied voltage,and the strength thereof depends upon the strength of the electric field(the level of the applied voltage). Therefore, when the electric fieldstrength is small (i.e., when the applied voltage is low), theorientation-regulating force exerted by the inclined electric field isweak, in which case the radially-inclined orientation may collapse dueto floating of the liquid crystal material when a stress is applied tothe liquid crystal panel. Once the radially-inclined orientationcollapses, it is not restored until application of a voltage sufficientto produce an inclined electric field that exerts a sufficiently strongorientation-regulating force. On the other hand, theorientation-regulating force from the side surface 40 s of theprotrusion 40 is exerted regardless of the applied voltage, and is verystrong as it is known in the art as the “anchoring effect” of thealignment film. Therefore, even when floating of the liquid crystalmaterial occurs and the radially-inclined orientation once collapses,the liquid crystal molecules 30 a in the vicinity of the side surface 40s of the protrusion 40 retain the same orientation direction as that ofthe radially-inclined orientation. Therefore, the radially-inclinedorientation is easily restored once the floating of the liquid crystalmaterial stops.

[0217] Thus, the liquid crystal display device 200 has an additionaladvantage of being strong against a stress in addition to the advantagesof the liquid crystal display device 100. Therefore, the liquid crystaldisplay device 200 can be suitably used in apparatuses that are oftensubject to a stress, such as PCs that are often carried around and PDAs.

[0218] When the protrusion 40 is made of a dielectric material having ahigh transparency, there is obtained an advantage of improving thecontribution to the display of a liquid crystal domain that is formed ina region corresponding to the opening 14 a. When the protrusion 40 ismade of an opaque dielectric material, there is obtained an advantagethat it is possible to prevent light leakage caused by the retardationof the liquid crystal molecules 30 a that are in an inclined orientationdue to the side surface 40 s of the protrusion 40. Whether to employ atransparent dielectric material or an opaque dielectric material can bedetermined in view of the application of the liquid crystal displaydevice, for example. In either case, the use of a photosensitive resinprovides an advantage that the step of patterning the protrusions 40corresponding to the openings 14 a can be simplified.

[0219] As described above, the liquid crystal display device 200includes the protrusion 40 in the opening 14 a of the picture elementelectrode 14, and the side surface 40s of the protrusion 40 exerts anorientation-regulating force in the same direction as that of theorientation-regulating force exerted by an inclined electric field forthe liquid crystal molecules 30 a of the liquid crystal layer 30.Preferred conditions for the side surface 40 s to exert anorientation-regulating force of the same direction as that of theorientation-regulating force exerted by the inclined electric field willnow be described with reference to FIG. 18A to FIG. 18C.

[0220]FIG. 18A to FIG. 18C schematically illustrate cross-sectionalviews of liquid crystal display devices 200A, 200B and 200C,respectively. FIG. 18A to FIG. 18C correspond to FIG. 17A. The liquidcrystal display devices 200A, 200B and 200C all have a protrusion in theopening 14 a, but differ from the liquid crystal display device 200 interms of the positional relationship between the entire protrusion 40 asa single structure and the corresponding opening 14 a.

[0221] In the liquid crystal display device 200 described above, theentire protrusion 40 as a structure is formed in the opening 14 a, andthe bottom surface of the protrusion 40 is smaller than the opening 14a, as illustrated in FIG. 17A. In the liquid crystal display device 200Aillustrated in FIG. 18A, the bottom surface of a protrusion 40A isaligned with the opening 14 a. In the liquid crystal display device 200Billustrated in FIG. 18B, the bottom surface of a protrusion 40B isgreater than the opening 14 a so as to cover a portion of the solidportion (conductive film) 14 b surrounding the opening 14 a. The solidportion 14 b is not formed on the side surface 40 s of any of theprotrusions 40, 40A and 40B. As a result, the equipotential lines EQ aresubstantially flat over the solid portion 14 b and drop into the opening14 a, as illustrated in the respective figures. Therefore, as theprotrusion 40 of the liquid crystal display device 200, the side surface40 s of the protrusion 40A of the liquid crystal display device 200A andthat of the protrusion 40B of the liquid crystal display device 200Bboth exert an orientation-regulating force of the same direction as thatof the orientation-regulating force exerted by the inclined electricfield, thereby stabilizing the radially-inclined orientation.

[0222] In contrast, in the liquid crystal display device 200Cillustrated in FIG. 18C, the bottom surface of a protrusion 40C isgreater than the opening 14 a, and a portion of the solid portion 14 bextending into a region above the opening 14 a is formed on the sidesurface 40s of the protrusion 40 c. Due to the influence of the portionof the solid portion 14 b formed on the side surface 40 s, a ridgeportion is created in the equipotential lines EQ. The ridge portion ofthe equipotential lines EQ has a gradient opposite to that of the otherportion of the equipotential lines EQ dropping into the opening 14 a.This indicates that an inclined electric field has been produced whosedirection is opposite to that of an inclined electric field fororienting the liquid crystal molecules 30 a into a radially-inclinedorientation. Therefore, in order for the side surface 40 s to have anorientation-regulating force of the same direction as that of theorientation-regulating force exerted by the inclined electric field, itis preferred that the solid portion (conductive film) 14 b is not formedon the side surface 40 s.

[0223] Next, a cross-sectional structure of the protrusion 40 takenalong line 19A-19A′ of FIG. 15A will be described with reference to FIG.19.

[0224] Since the protrusions 40 illustrated in FIG. 15A are formed so asto completely surround each unit solid portion 14 b′ in a generallycircular pattern, as described above, the portions serving to connectadjacent unit solid portions 14 b′ together (the branch portionsextending in four directions from the circular portion) are formed onthe protrusion 40 as illustrated in FIG. 19. Therefore, in the step ofdepositing the conductive film to be the solid portions 14 b of thepicture element electrode 14, there is a considerable possibility thatdisconnection may occur on the protrusion 40 or delamination may occurin an after-treatment of the production process.

[0225] In view of this, in a liquid crystal display device 200Dillustrated in FIG. 20A and FIG. 20B, protrusions 40D independent of oneanother are formed so that each of the protrusions 40D is completelyincluded within the opening 14 a so that the conductive film to be thesolid portion 14 b is formed on the flat surface of the substrate 11,thereby eliminating the possibility of disconnection or delamination.Although the protrusions 40D do not completely surround each unit solidportion 14 b′ in a generally circular pattern, a generally circularliquid crystal domain corresponding to each unit solid portion 14 b′ isformed, and the radially-inclined orientation of the unit solid portion14 b′ is stabilized as in the above-described examples.

[0226] The effect of stabilizing the radially-inclined orientation whichis obtained by forming the protrusion 40 in the opening 14 a is notlimited to the pattern of the opening 14 a described above, but maysimilarly be applied to any of the patterns of the opening 14 adescribed above to obtain effects as those described above. In order forthe protrusion 40 to sufficiently exert the effect of stabilizing theorientation against a stress, it is preferred that the pattern of theprotrusion 40 (the pattern as viewed in the substrate normal direction)covers as much area as possible of the liquid crystal layer 30.Therefore, for example, a greater orientation stabilizing effect of theprotrusion 40 can be obtained with the positive pattern with circularunit solid portions 14 b′ than with the negative pattern with circularopenings 14 a.

[0227] In order to obtain a sufficient orientation-regulating force suchthat an after image due to a stress is not observed even when a stressis applied to the liquid crystal panel, by providing the protrusion 40without providing the second orientation-regulating structure to bedescribed later, the height of the protrusion 40 is preferably in therange of about 0.5 μm to about 2 μm, when the thickness of the liquidcrystal layer 30 is about 3 μm. Typically, the height of the protrusion40 is preferably in the range of about ⅙ to about ⅔ of the thickness ofthe liquid crystal layer 30. However, since the liquid crystal moleculeswhose orientation is regulated by the orientation-regulating force ofthe side surface of the protrusion 40 have a poor response to an appliedvoltage (a small retardation change in response to the applied voltage),the protrusion may decrease the contrast ratio of the display.Therefore, it is preferred that the size, the height and the number ofprotrusions are set so as not to decrease the display quality.

[0228] With the electrode arrangement described above where openings areprovided in one of a pair of electrodes, a sufficient voltage may not beapplied across the liquid crystal layer in a region corresponding to theopening and a sufficient retardation change may not be obtained, therebydecreasing the light efficiency. In view of this, a dielectric layer maybe provided on one side of the electrode with openings (an upperelectrode) that is away from the liquid crystal layer, with anadditional electrode (a lower electrode) being provided via thedielectric layer so as to at least partially oppose the electrodeopenings (i.e., a two-layer electrode may be employed). In this way, itis possible to apply a sufficient voltage across the liquid crystallayer corresponding to the opening, thereby improving the lightefficiency and/or the response characteristic.

[0229] Each of FIG. 21A to FIG. 21C schematically illustrates across-sectional structure of one picture element region of a liquidcrystal display device 300 having a picture element electrode 15 (atwo-layer electrode) including a lower electrode 12, an upper electrode14, and a dielectric layer 13 provided therebetween. The upper electrode14 of the picture element electrode 15 is substantially equivalent tothe picture element electrode 14 described above, and includes openingshaving any of the various shapes described above and arranged in any ofthe various patterns described above. The function of the pictureelement electrode 15 having a two-layer structure will now be described.

[0230] The picture element electrode 15 of the liquid crystal displaydevice 300 includes a plurality of openings 14 a (including 14 a 1 and14 a 2). FIG. 21A schematically illustrates an orientation of the liquidcrystal molecules 30 a in the liquid crystal layer 30 in the absence ofan applied voltage (OFF state). FIG. 21B schematically illustrates astate where the orientation of the liquid crystal molecules 30 a hasjust started to change (initial ON state) according to the voltageapplied across the liquid crystal layer 30. FIG. 21C schematicallyillustrates a state where the orientation of the liquid crystalmolecules 30 a has changed and become steady according to the appliedvoltage. In FIG. 21A to FIG. 21C, the lower electrode 12, which isprovided so as to oppose the openings 14 a 1 and 14 a 2 via thedielectric layer 13, overlaps both of the openings 14 a 1 and 14 a 2 andalso extends in a region between the openings 14 a 1 and 14 a 2 (aregion where the upper electrode 14 exists). However, the arrangement ofthe lower electrode 12 is not limited to this, but the arrangement mayalternatively be such that the area of the lower electrode 12=the areaof the opening 14 a, or the area of the lower electrode 12<the area ofthe opening 14 a, for each of the openings 14 a 1 and 14 a 2. Thus, thestructure of the lower electrode 12 is not limited to any particularstructure as long as the lower electrode 12 opposes at least a portionof the opening 14 a via the dielectric layer 13. However, when the lowerelectrode 12 is provided within the opening 14 a, there is a region (gapregion) in which neither the lower electrode 12 nor the upper electrode14 is present in a plane as viewed in the direction normal to thesubstrate 11. A sufficient voltage may not be applied across the liquidcrystal layer 30 in the region opposing the gap region. Therefore, inorder to stabilize the orientation of the liquid crystal layer 30, it ispreferred that the width of the gap region is sufficiently reduced.Typically, it is preferred that the width of the gap region does notexceed about 4 μm. Moreover, the lower electrode 12 that is provided ata position such that it opposes the region where the conductive layer ofthe upper electrode 14 exists via the dielectric layer 13 hassubstantially no influence on the electric field applied across theliquid crystal layer 30. Therefore, such a lower electrode 12 may or maynot be patterned.

[0231] As illustrated in FIG. 21A, when the picture element electrode 15and the counter electrode 22 are at the same potential (a state where novoltage is applied across the liquid crystal layer 30), the liquidcrystal molecules 30 a in the picture element region are alignedvertical to the surfaces of the substrates 11 and 21. Herein, it isassumed that the upper electrode 14 and the lower electrode 12 of thepicture element electrode 15 are at the same potential for the sake ofsimplicity.

[0232] When a voltage is applied across the liquid crystal layer 30, apotential gradient represented by equipotential lines EQ shown in FIG.21B is produced. A uniform potential gradient represented byequipotential lines EQ parallel to the surfaces of the upper electrode14 and the counter electrode 22 is produced in the liquid crystal layer30 in a region between the upper electrode 14 of the picture elementelectrode 15 and the counter electrode 22. A potential gradientaccording to the potential difference between the lower electrode 12 andthe counter electrode 22 is produced in regions of the liquid crystallayer 30 located above the openings 14 a 1 and 14 a 2 of the upperelectrode 14. The potential gradient produced in the liquid crystallayer 30 is influenced by a voltage drop due to the dielectric layer 13,whereby the equipotential lines EQ in the liquid crystal layer 30 dropin regions corresponding to the openings 14 a 1 and 14 a 2 (creating aplurality of “troughs” in the equipotential lines EQ). Since the lowerelectrode 12 is provided in a region opposing the openings 14 a 1 and 14a 2 via the dielectric layer 13, the liquid crystal layer 30 around therespective central portions of the openings 14 a 1 and 14 a 2 also has apotential gradient that is represented by a portion of the equipotentiallines EQ parallel to the plane of the upper electrode 14 and the counterelectrode 22 (“the bottom of the trough” of the equipotential lines EQ).An inclined electric field represented by an inclined portion of theequipotential lines EQ is produced in the liquid crystal layer 30 abovean edge portion EG of each of the openings 14 a 1 and 14 a 2 (theperipheral portion of and within the opening including the boundarythereof).

[0233] As is clear from a comparison between FIG. 21B and FIG. 2A, sincethe liquid crystal display device 300 has the lower electrode 12, asufficient electric field can act also upon the liquid crystal moleculesin the liquid crystal domain formed in a region corresponding to theopening 14 a.

[0234] A torque acts upon the liquid crystal molecules 30 a having anegative dielectric anisotropy so as to direct the axial orientation ofthe liquid crystal molecules 30 a to be parallel to the equipotentiallines EQ. Therefore, the liquid crystal molecules 30 a above the rightedge portion EG in FIG. 21B incline (rotate) clockwise and the liquidcrystal molecules 30 a above the left edge portion EG incline (rotate)counterclockwise as indicated by arrows in FIG. 21B. As a result, theliquid crystal molecules 30 a above the edge portions EG are orientedparallel to the corresponding portions of the equipotential lines EQ.

[0235] When an electric field represented by a portion of theequipotential lines EQ inclined with respect to the axial orientation ofthe liquid crystal molecules 30 a (an inclined electric field) isproduced at the edge portions EG of the openings 14 a 1 and 14 a 2 ofthe liquid crystal display device 300, as illustrated in FIG. 21B, theliquid crystal molecules 30 a incline in whichever direction (thecounterclockwise direction in the illustrated example) that requiresless rotation for the liquid crystal molecules 30 a to be parallel tothe equipotential line EQ, as illustrated in FIG. 3B. The liquid crystalmolecules 30 a in a region where an electric field represented by anequipotential line EQ perpendicular to the axial orientation of theliquid crystal molecules 30 a is produced incline in the same directionas the liquid crystal molecules 30 a located on the inclined portion ofthe equipotential lines EQ so that the orientation thereof is continuous(in conformity) with the orientation of the liquid crystal molecules 30a located on the inclined portion of the equipotential lines EQ asillustrated in FIG. 3C.

[0236] The change in the orientation of the liquid crystal molecules 30a, starting from those that are located on the inclined portion of theequipotential lines EQ, proceeds as described above and reaches a steadystate, i.e., an inclined orientation (radially-inclined orientation)that is symmetric about the center SA of each of the openings 14 a 1 and14 a 2, as schematically illustrated in FIG. 21C. The liquid crystalmolecules 30 a in a region of the upper electrode 14 located between thetwo adjacent openings 14 a 1 and 14 a 2 also take an inclinedorientation so that the orientation thereof is continuous (inconformity) with the orientation of the liquid crystal molecules 30 a atthe edge portions of the openings 14 a 1 and 14 a 2. The liquid crystalmolecules 30 a in the middle between the edge of the opening 14 a 1 andthe edge of the opening 14 a 2 are subject to substantially the sameinfluence from the liquid crystal molecules 30 a at the respective edgeportions, and thus remain in a vertical alignment as the liquid crystalmolecules 30 a located around the central portion of each of theopenings 14 a 1 and 14 a 2.

[0237] As a result, the liquid crystal layer above the upper electrode14 between the adjacent two openings 14 a 1 and 14 a 2 also takes aradially-inclined orientation. Note that the inclination direction ofthe liquid crystal molecules differs between the radially-inclinedorientation of the liquid crystal layer in each of the openings 14 a 1and 14 a 2 and that of the liquid crystal layer between the openings 14a 1 and 14 a 2. Observation of the orientation around the liquid crystalmolecule 30 a at the center of each region having the radially-inclinedorientation illustrated in FIG. 21C shows that the liquid crystalmolecules 30 a in the regions of the openings 14 a 1 and 14 a 2 areinclined so as to form a cone that spreads toward the counter electrode,whereas the liquid crystal molecules 30 a in the region between theopenings are inclined so as to form a cone that spreads toward the upperelectrode 14. Since both of these radially-inclined orientations areformed so as to conform with the inclined orientation of the liquidcrystal molecules 30 a at an edge portion, the two radially-inclinedorientations are continuous with each other.

[0238] As described above, when a voltage is applied across the liquidcrystal layer 30, the liquid crystal molecules 30 a incline, startingfrom those above the respective edge portions EG of the openings 14 a 1and 14 a 2 provided in the upper electrode 14. Then, the liquid crystalmolecules 30 a in the surrounding regions incline so as to conform withthe inclined orientation of the liquid crystal molecules 30 a above theedge portion EG. Thus, a radially-inclined orientation is formed.Therefore, as the number of openings 14 a to be provided in each pictureelement region increases, the number of liquid crystal molecules 30 athat initially start inclining in response to an applied electric fieldalso increases, thereby reducing the amount of time that is required toachieve the radially-inclined orientation across the entire pictureelement region. Thus, by increasing the number of openings 14 a to beprovided in the picture element electrode 15 for each picture elementregion, it is possible to improve the response speed of a liquid crystaldisplay device. Moreover, By employing a two-layer electrode includingthe upper electrode 14 and the lower electrode 12 as the picture elementelectrode 15, a sufficient electric field can act also upon the liquidcrystal molecules in a region corresponding to the opening 14 a, therebyimproving the response characteristic of the liquid crystal displaydevice.

[0239] The dielectric layer 13 provided between the upper electrode 14and the lower electrode 12 of the picture element electrode 15 mayinclude an opening (aperture) or a depressed portion in the opening 14 aof the upper electrode 14. In other words, in the two-layer pictureelement electrode 15, the whole of a region of the dielectric layer 13located in the opening 14 a of the upper electrode 14 may be removed(thereby forming an opening therein) or a portion of such a region maybe removed (thereby forming a depressed portion).

[0240] First, the structure and operation of a liquid crystal displaydevice 400 having such a picture element electrode 14 which includes anopening in the dielectric layer 13 will be described with reference toFIG. 22A to FIG. 22C. A single opening 14 a provided in the upperelectrode 14 will be described below for the sake of simplicity.

[0241] In the liquid crystal display device 400, the upper electrode 14of the picture element electrode 15 includes the opening 14 a, and thedielectric layer 13 provided between the lower electrode 12 and theupper electrode 14 includes an opening 13 a formed so as to correspondto the opening 14 a of the upper electrode 14, with the lower electrode12 being exposed through the opening 13 a. The side wall of the opening13 a of the dielectric layer 13 is typically tapered. The liquid crystaldisplay device 400 has substantially the same structure as that of theliquid crystal display device 300 except that the dielectric layer 13includes the opening 13 a, and the two-layer picture element electrode15 functions in substantially the same manner as the picture elementelectrode 15 of the liquid crystal display device 300, to form a liquidcrystal domain in the liquid crystal layer 30 that takes aradially-inclined orientation in the presence of an applied voltage.

[0242] The operation of the liquid crystal display device 400 will bedescribed with reference to FIG. 22A to FIG. 22C. FIG. 22A to FIG. 22Crespectively correspond to FIG. 1A to FIG. 1C illustrating the liquidcrystal display device 100.

[0243] As illustrated in FIG. 22A, the liquid crystal molecules 30 a ineach picture element region are aligned vertical to the surfaces of thesubstrates 11 and 21 in the absence of an applied voltage (OFF state).In the following description, the orientation-regulating force from theside wall of the opening 13 a will be ignored for the sake ofsimplicity.

[0244] When a voltage is applied across the liquid crystal layer 30, apotential gradient represented by equipotential lines EQ shown in FIG.22B is produced. As can be seen from the drop of the equipotential linesEQ (creating a “trough” therein) in a region corresponding to theopening 14 a of the upper electrode 14, an inclined electric field isproduced in the liquid crystal layer 30 of the liquid crystal displaydevice 400 as in the potential gradient illustrated in FIG. 21B.However, since the dielectric layer 13 of the picture element electrode15 includes the opening 13 a in a region corresponding to the opening 14a of the upper electrode 14, the voltage applied across the region ofthe liquid crystal layer 30 corresponding to the opening 14 a (theopening 13 a) is exactly the potential difference between the lowerelectrode 12 and the counter electrode 22, and the voltage drop(capacitance division) due to the dielectric layer 13 does not occur. Inother words, all of the seven equipotential lines EQ drawn in FIG. 22Bbetween the upper electrode 14 and the counter electrode 22 stay betweenthe upper electrode 14 and the counter electrode 22 across the entireliquid crystal layer 30 (as opposed to FIG. 21B where one of the fiveequipotential lines EQ is drawn into the dielectric layer 13), therebyapplying a constant voltage across the entire picture element region.

[0245] Thus, by providing the opening 13 a in the dielectric layer 13,it is possible to apply the same voltage across the region of the liquidcrystal layer 30 corresponding to the opening 13 a as that appliedacross the other regions of the liquid crystal layer 30. However, thethickness of the liquid crystal layer 30, across which a voltage isapplied, varies depending upon the location in each picture elementregion, whereby the change in retardation in the presence of an appliedvoltage also varies depending upon the location. If the degree ofvariation is significant, the display quality may deteriorate.

[0246] In the structure illustrated in FIG. 22A to FIG. 22C, thethickness d1 of the liquid crystal layer 30 on the upper electrode (thesolid portion excluding the opening 14 a) 14 and the thickness d2 of theliquid crystal layer 30 on the lower electrode 12 exposed through theopening 14 a (and the opening 13 a) differ from each other by thethickness of the dielectric layer 13. When the portion of the liquidcrystal layer 30 having the thickness d1 and the other portion of theliquid crystal layer 30 having the thickness d2 are driven with the samevoltage range, the amount of retardation change caused by theorientation change in the liquid crystal layer 30 varies therebetween bythe influence of the difference in thickness between the respectiveportions of the liquid crystal layer 30. When the relationship betweenthe applied voltage and the amount of retardation of the liquid crystallayer 30 considerably varies depending upon the location, the followingproblem arises. That is, in a design where the display quality is givena higher priority, the transmittance is sacrificed, and when thetransmittance is given a higher priority, the color temperature of thewhite display shifts, thereby sacrificing the display quality.Therefore, when the liquid crystal display device 400 is used as atransmission type liquid crystal display device, the thickness of thedielectric layer 13 is preferably small.

[0247] Next, a cross-sectional structure of one picture element regionof a liquid crystal display device 500 in which the dielectric layer ofthe picture element electrode includes a depressed portion will bedescribed with reference to FIG. 23.

[0248] The dielectric layer 13 of the picture element electrode 15 ofthe liquid crystal display device 500 includes a depressed portion 13 bcorresponding to the opening 14 a of the upper electrode 14. Other thanthis, the structure of the liquid crystal display device 500 issubstantially the same as that of the liquid crystal display device 400illustrated in FIG. 22A to FIG. 22C.

[0249] In the liquid crystal display device 500, a portion of thedielectric layer 13 located in the opening 14 a of the upper electrode14 of the picture element electrode 15 is not completely removed,whereby the thickness d3 of a portion of the liquid crystal layer 30located in the opening 14 a is smaller than the thickness d2 of thecorresponding portion of the liquid crystal layer 30 located in theopening 14 a of the liquid crystal display device 400 by the thicknessof the dielectric layer 13 in the depressed portion 13 b. Moreover, thevoltage applied across the region of the liquid crystal layer 30 in theopening 14 a is subject to the voltage drop (capacitance division) dueto the dielectric layer 13 in the depressed portion 13 b, and thus islower than the voltage applied across the region of the liquid crystallayer 30 on the upper electrode (the region thereof excluding theopening 14 a) 14. Therefore, by adjusting the thickness of thedielectric layer 13 in the depressed portion 13 b, it is possible tocontrol the relationship between the variations in retardation amountdue to the difference in thickness of the liquid crystal layer 30 andthe variations in the applied voltage across the liquid crystal layer 30depending upon the location (the amount of decrease in the voltageapplied across the liquid crystal layer in the opening 14 a), so as toensure that the relationship between the applied voltage and theretardation does not depend upon the location in the picture elementregion. More strictly, the relationship between the applied voltage andthe retardation can be controlled to be uniform across the pictureelement region, thereby realizing a high-quality display, by adjustingthe birefringence of the liquid crystal layer, the thickness of theliquid crystal layer, the dielectric constant and the thickness of thedielectric layer, and the thickness (or depth) of the depressed portionof the dielectric layer. Particularly, as compared to a transmissiontype liquid crystal display device having a flat-surface dielectriclayer, there is an advantage that the decrease in transmittance due to adecrease in the voltage applied across the region of the liquid crystallayer 30 corresponding to the opening 14 a of the upper electrode 14(the decrease in the light efficiency) is suppressed.

[0250] In the above description, the same voltage is applied to theupper electrode 14 and the lower electrode 12 of the picture elementelectrode 15. When different voltages are applied to the lower electrode12 and the upper electrode 14, it is possible to increase the variety ofstructures of liquid crystal display devices capable of displaying animage without display non-uniformity. For example, in the structurewhere the dielectric layer 13 is provided in the opening 14 a of theupper electrode 14, a voltage higher than the voltage applied to theupper electrode 14 by the voltage drop due to the dielectric layer 13 isapplied to the lower electrode 12, whereby it is possible to prevent thevoltage applied across the liquid crystal layer 30 from varyingdepending upon the location in the picture element region.

[0251] The liquid crystal display device having the picture elementelectrode 15 of the two-layer structure may be a transmission-reflectiontype liquid crystal display device (see, for example, Japanese Laid-OpenPatent Publication No. 11-101992) as well as a transmission orreflection type liquid crystal display device.

[0252] A transmission-reflection type liquid crystal display device(hereinafter, referred to simply as a “two-way liquid crystal displaydevice”) refers to a liquid crystal display device that includes, ineach picture element region, a transmission region T displaying an imagein a transmission mode and a reflection region R displaying an image ina reflection mode (see FIG. 21A). Typically, the transmission region Tand the reflection region R are defined respectively by a transparentelectrode and a reflection electrode. The reflection region can bedefined by a structure using a combination of a reflection layer and atransparent electrode instead of the reflection electrode.

[0253] In the two-way liquid crystal display device, an image can bedisplayed in either the reflection mode or the transmission mode whichcan be switched from one to another, or an image can be displayed inboth display modes at the same time. Therefore, for example, thereflection mode display can be used under an environment with brightambient light, and the transmission mode display can be used under adark environment. When both of these display modes are used at the sametime, it is possible to suppress the decrease in the contrast ratiowhich is observed when a transmission mode liquid crystal display deviceis used under an environment with bright ambient light (a state wherelight from a fluorescent lamp or sun light is directly incident upon thedisplay plane at a certain angle). Thus, the two-way liquid crystaldisplay device can compensate for the drawback of a transmission typeliquid crystal display device. The ratio between the area of thetransmission region T and that of the reflection region R can besuitably determined according to the application of the liquid crystaldisplay device. For a liquid crystal display device that is usedexclusively as a transmission type display device, the area ratio of thereflection region can be reduced to such a degree that an image cannotbe displayed in a reflection mode, and it is still possible tocompensate for the drawback of a transmission type liquid crystaldisplay device described above.

[0254] A two-way liquid crystal display device can be obtained by, forexample, employing a reflection electrode and a transparent electrode asthe upper electrode 14 and the lower electrode 12, respectively, of theliquid crystal display device 300 as illustrated in FIG. 21A. Thetwo-way liquid crystal display device is not limited to this example,but may alternatively be obtained by employing a transparent conductivelayer as either one of the upper electrode 14 and the lower electrode 12of the liquid crystal display device while employing a reflectionconductive layer as the other. Note that in order for thevoltage-transmittance characteristics of a display in the reflectionmode and those of a display in the transmission mode to conform witheach other, it is preferred that the thickness of the liquid crystallayer 30 in the reflection region R (e.g., d1 in FIG. 22A) is about onehalf of the thickness of the liquid crystal layer 30 in the transmissionregion T (e.g., d2 in FIG. 22B). of course, the voltage to be applied tothe upper electrode 14 and the voltage to be applied to the lowerelectrode 12 may be adjusted, instead of adjusting the thickness of theliquid crystal layer.

[0255] Second Orientation-regulating Structure

[0256] Next, the specific structure and function of the secondorientation-regulating structure will be described. A case where thefirst orientation-regulating structure is provided on the TFT substrateand the second orientation-regulating structure is provided on thecounter substrate will be described below in conformity with theexamples illustrated above. In addition to the structure for aligningthe liquid crystal molecules vertical to the substrate plane (e.g., thevertical alignment film provided on one side of each of the pair ofsubstrates that is closer to the liquid crystal layer), the liquidcrystal display device of the present invention includes the firstorientation-regulating structure as described above for orienting theliquid crystal molecules into a radially-inclined orientation, and thesecond orientation-regulating structure for orienting the liquid crystalmolecules into a radially-inclined orientation in cooperation with thefirst orientation-regulating structure (stabilizing theradially-inclined orientation) as will be described later.

[0257]FIG. 24A to FIG. 24E schematically illustrate a counter substrate600 b having a second orientation-regulating structure 28. Each elementhaving substantially the same function as that of the liquid crystaldisplay devices described above will be denoted by the same referencenumeral and will not be further described.

[0258] The second orientation-regulating structure 28 illustrated inFIG. 24A to FIG. 24E functions to orient the liquid crystal molecules 30a of the liquid crystal layer 30 into a radially-inclined orientation.Note that the second orientation-regulating structure 28 illustrated inFIG. 24A to FIG. 24D and that illustrated in FIG. 24E are different interms of the direction in which the liquid crystal molecules 30 a are tobe inclined.

[0259] The direction in which the liquid crystal molecules are inclinedby the second orientation-regulating structure 28 illustrated in FIG.24A to FIG. 24D is aligned with the orientation direction of theradially-inclined orientation of each liquid crystal domain that isformed by the first orientation-regulating structure in a regioncorresponding to the unit solid portion 14 b′ (see, for example, FIG. 1Aand FIG. 1B) of the picture element electrode 14. In contrast, thedirection in which the liquid crystal molecules are inclined by thesecond orientation-regulating structure 28 illustrated in FIG. 24E isaligned with the orientation direction of the radially-inclinedorientation of each liquid crystal domain that is formed by the firstorientation-regulating structure in a region corresponding to theopening 14 a (see, for example, FIG. 1A and FIG. 1B) of the pictureelement electrode 14.

[0260] The second orientation-regulating structure. 28 illustrated inFIG. 24A is formed by an opening 22 a of the counter electrode 22 andthe solid portion 14 b of the picture element electrode (or an upperelectrode; not shown in FIG. 24A; see, for example, FIG. 1A) 14 which isprovided so as to oppose the opening 22 a. A vertical alignment film(not shown) is provided on one surface of the counter substrate 600 bthat is closer to the liquid crystal layer 30.

[0261] The second orientation-regulating structure 28, as the firstorientation-regulating structure described above, exerts anorientation-regulating force only in the presence of an applied voltage.Since the second orientation-regulating structure 28 is only required toexert an orientation-regulating force upon the liquid crystal moleculesin each liquid crystal domain in a radially-inclined orientation formedby the first orientation-regulating structure, the size of the opening22 a is smaller than the opening 14 a provided in the picture elementelectrode 14, and smaller than the unit solid portion 14 b′ (see, forexample, FIG. 1A) which is surrounded by the openings 14 a. For example,a sufficient effect can be obtained only with an area less than or equalto one half of that of the opening 14 a or the unit solid portion 14 b′.When the opening 22 a of the counter electrode 22 is provided so as tooppose the central portion of the unit solid portion 14 b′ of thepicture element electrode 14, the continuity of the orientation of theliquid crystal molecules increases, and it is possible to fix theposition of the central axis of the radially-inclined orientation.

[0262] As described above, when a structure exerting anorientation-regulating force only in the presence of an applied voltageis employed as the second orientation-regulating structure,substantially all of the liquid crystal molecules 30 a of the liquidcrystal layer 30 take a vertical alignment in the absence of an appliedvoltage. Therefore, when employing a normally black mode, substantiallyno light leakage occurs in a black display, thereby realizing a displaywith a desirable contrast ratio.

[0263] However, in the absence of an applied voltage, theorientation-regulating force is not exerted and thus theradially-inclined orientation is not formed. Moreover, when the appliedvoltage is low, there is only a weak orientation-regulating force,whereby an after image may be observed when a considerable stress isapplied upon the liquid crystal panel.

[0264] Each of the second orientation-regulating structures 28illustrated in FIG. 24B to FIG. 24D exerts an orientation-regulatingforce regardless of the presence/absence of an applied voltage, wherebyit is possible to obtain a stable radially-inclined orientation at anydisplay gray level, and there is provided a high resistance to a stress.

[0265] First, the second orientation-regulating structure 28 illustratedin FIG. 24B includes a protrusion 22 b that is provided on the counterelectrode 22 so as to protrude into the liquid crystal layer 30. Whilethere is no particular limitation on the material of the protrusion 22b, the protrusion 22 b can be easily provided by using a dielectricmaterial such as a resin. A vertical alignment film (not shown) isprovided on one surface of the counter substrate 600 b that is closer tothe liquid crystal layer 30. The protrusion 22 b orients the liquidcrystal molecules 30 a into a radially-inclined orientation by virtue ofthe configuration of the surface thereof (with a vertical alignmentpower). It is preferred to use a resin material that deforms by heat, inwhich case it is possible to easily form the protrusion 22 b having aslightly-humped cross section as illustrated in FIG. 24B through a heattreatment after patterning. The protrusion 22 b having a slightly-humpedcross section with a vertex (e.g., a portion of a sphere) as illustratedin the figure or a conical protrusion provides a desirable effect offixing the central position of the radially-inclined orientation.

[0266] The second orientation-regulating structure 28 illustrated inFIG. 24C is provided as a surface having a horizontal alignment powerfacing the liquid crystal layer 30 that is provided in an opening (or adepressed portion) 23 a in a dielectric layer 23 formed under thecounter electrode 22 (i.e., on one side of the counter electrode 22 thatis closer to the substrate 21). A vertical alignment film 24 is providedso as to cover one side of the counter substrate 600 b that is closer tothe liquid crystal layer 30 while leaving a region corresponding to theopening 23 a uncovered, whereby the surface in the opening 23 afunctions as a horizontal alignment surface. Alternatively, a horizontalalignment film 25 may be provided only in the opening 23 a asillustrated in FIG. 24D.

[0267] The horizontal alignment film illustrated in FIG. 24D can beprovided by, for example, once providing the vertical alignment film 24across the entire surface of the counter substrate 600 b, and thenselectively irradiating a portion of the vertical alignment film 24 inthe opening 23 a with UV light so as to reduce the vertical alignmentpower thereof. The horizontal orientation power required for the secondorientation-regulating structure 28 does not have to be so high that theresulting pretilt angle is as small as that resulting from an alignmentfilm used in a TN type liquid crystal display device. For example, apretilt angle of 45° or less is sufficient.

[0268] As illustrated in FIG. 24C and FIG. 24D, on the horizontalorientation surface in the opening 23 a, the liquid crystal molecules 30a are urged to be horizontal with respect to the substrate plane. As aresult, the liquid crystal molecules 30 a form an orientation that iscontinuous with the orientation of the surrounding, vertically alignedliquid crystal molecules 30 a on the vertical alignment film 24, therebyobtaining a radially-inclined orientation as illustrated in the figure.

[0269] A radially-inclined orientation can be obtained only byselectively providing a horizontal orientation surface (e.g., thesurface of the electrode, or a horizontal alignment film) on the flatsurface of the counter electrode 22 without providing a depressedportion (that is formed by the opening in the dielectric layer 23) onthe surface of the counter electrode 22. However, the radially-inclinedorientation can be further stabilized by virtue of the surfaceconfiguration of the depressed portion.

[0270] It is preferred to use a color filter layer or an overcoat layerof a color filter layer as the dielectric layer 23, for example, to formthe depressed portion in the surface of the counter substrate 600 b thatis closer to the liquid crystal layer 30, because it adds nothing to theprocess. In the structures illustrated in FIG. 24C and FIG. 24D, thereis little decrease in light efficiency because there is no region wherea voltage is applied across the liquid crystal layer 30 via theprotrusion 22 b as in the structure illustrated in FIG. 24A.

[0271] In the second orientation-regulating structure 28 illustrated inFIG. 24E, a depressed portion is formed on one side of the countersubstrate 600 b that is closer to the liquid crystal layer 30 by usingthe opening 23 a of the dielectric layer 23, as in the secondorientation-regulating structure 28 illustrated in FIG. 24D, and ahorizontal alignment film 26 is formed only in the bottom portion of thedepressed portion. Instead of forming the horizontal alignment film 26,the surface of the counter electrode 22 may be exposed as illustrated inFIG. 24C.

[0272] A liquid crystal display device 600 having the firstorientation-regulating structure and the second orientation-regulatingstructure as described above is shown in FIG. 25A and FIG. 25B. FIG. 25Ais a plan view, and FIG. 25B is a cross-sectional view taken along line25B-25B′ of FIG. 25A.

[0273] The liquid crystal display device 600 includes the TFT substrate100 a having the picture element electrode 14 with the openings 14 abeing the first orientation-regulating structure, and the countersubstrate 600 b which includes the second orientation-regulatingstructure 28. The first orientation-regulating structure is not limitedto the structure illustrated herein, but may be any other structuredescribed above. Moreover, while a structure that exerts anorientation-regulating force even in the absence of an applied voltage(FIG. 24B to FIG. 24D and FIG. 24E) will be used as the secondorientation-regulating structure 28, the second orientation-regulatingstructure illustrated in FIG. 24B to FIG. 24D can be replaced with thatillustrated in FIG. 24A.

[0274] Among the second orientation-regulating structures 28 provided inthe counter substrate 600 b of the liquid crystal display device 600,the second orientation-regulating structure 28 provided around thecenter of a region opposing the solid portion 14 b of the pictureelement electrode 14 is one of those illustrated in FIG. 24B to FIG.24D, and the second orientation-regulating structure 28 provided aroundthe center of a region opposing the opening 14 a of the picture elementelectrode 14 is one illustrated in FIG. 24E.

[0275] With such an arrangement, in the presence of an applied voltageacross the liquid crystal layer 30, i.e., in the presence of an appliedvoltage between the picture element electrode 14 and the counterelectrode 22, the direction of the radially-inclined orientation formedby the first orientation-regulating structure is aligned with thedirection of the radially-inclined orientation formed by the secondorientation-regulating structure 28, thereby stabilizing theradially-inclined orientation. This is schematically shown in FIG. 26Ato FIG. 26C. FIG. 26A illustrates a state in the absence of an appliedvoltage, FIG. 26B illustrates a state where the orientation has juststarted to change (initial ON state) after application of a voltage, andFIG. 26C schematically illustrates a steady state during the voltageapplication.

[0276] As illustrated in FIG. 26A, the orientation-regulating forceexerted by the second orientation-regulating structure (FIG. 24B to FIG.24D) acts upon the liquid crystal molecules 30 a in the vicinity thereofeven in the absence of an applied voltage, thereby forming aradially-inclined orientation.

[0277] When voltage application begins, an electric field represented byequipotential lines EQ shown in FIG. 26B is produced (by the firstorientation-regulating structure), and a liquid crystal domain in whichthe liquid crystal molecules 30 a are in a radially-inclined orientationis formed in each region corresponding to the opening 14 a and eachregion corresponding to the solid portion 14 b, and the liquid crystallayer 30 reaches a steady state as illustrated in FIG. 26C. Theinclination direction of the liquid crystal molecules 30 a in eachliquid crystal domain coincides with the direction in which the liquidcrystal molecules 30 a are inclined by the orientation-regulating forceexerted by the second orientation-regulating structure 28 that isprovided in a corresponding region.

[0278] When a stress is applied upon the liquid crystal display device600 in a steady state, the radially-inclined orientation of the liquidcrystal layer 30 once collapses, but upon removal of the stress, theradially-inclined orientation is restored because of theorientation-regulating forces from the first orientation-regulatingstructure and the second orientation-regulating structure acting uponthe liquid crystal molecules 30 a. Therefore, the occurrence of an afterimage due to a stress is suppressed. When the orientation-regulatingforce from the second orientation-regulating structure 28 is excessivelystrong, retardation occurs even in the absence of an applied voltage dueto the radially-inclined orientation, whereby the display contrast ratiomay decrease. However, the orientation-regulating force from the secondorientation-regulating structure 28 does not have to be strong becauseit is only required to have an effect of stabilizing a radially-inclinedorientation formed by the first orientation-regulating structure andfixing the central axis position thereof. Therefore, anorientation-regulating force that would not cause such a degree ofretardation as to deteriorate the display quality is sufficient.

[0279] For example, when the protrusion 22 b illustrated in FIG. 24B isemployed, each protrusion 22 b may have a diameter of about 15 μm and aheight (thickness) of about 1 μm for the unit solid portion 14 b′ havinga diameter of about 30 μm to about 35 μm, thereby obtaining a sufficientorientation-regulating force and suppressing the reduction in thecontrast ratio due to retardation to a practical level.

[0280]FIG. 27A and FIG. 27B illustrate another liquid crystal displaydevice 700 including the first orientation-regulating structure and thesecond orientation-regulating structure.

[0281] The liquid crystal display device 700 does not have the secondorientation-regulating structure in a region opposing the opening 14 aof the picture element electrode 14 of the TFT substrate 100 a.Formation of the second orientation-regulating structure 28 illustratedin FIG. 24E which should be formed in a region opposing the opening 14 aintroduces difficulties into the process. Therefore, in view of theproductivity, it is preferred to use only one of the secondorientation-regulating structures 28 illustrated in FIG. 24A to FIG.24D. Particularly, the second orientation-regulating structure 28illustrated in FIG. 24B is preferred because it can be produced by asimple process.

[0282] Even if no second orientation-regulating structure is provided ina region corresponding to the opening 14 a as in the liquid crystaldisplay device 700, a radially-inclined orientation as that of theliquid crystal display device 600 is obtained, as schematicallyillustrated in FIG. 28A to FIG. 28C, and also the stress resistancethereof is at a practical level.

[0283] An example of a liquid crystal display device having the firstorientation-regulating structure and the second orientation-regulatingstructure is illustrated in FIG. 29A, FIG. 29B and FIG. 29C. FIG. 29A,FIG. 29B and FIG. 29C are cross-sectional views each schematicallyillustrating a liquid crystal display device 800 having the firstorientation-regulating structure and the second orientation-regulatingstructure. FIG. 29A illustrates a state in the absence of an appliedvoltage, FIG. 29B illustrates a state where the orientation has juststarted to change (initial ON state) after application of a voltage, andFIG. 29C schematically illustrates a steady state during the voltageapplication.

[0284] The liquid crystal display device 800 includes the protrusion 40illustrated in FIG. 17A and FIG. 17B in the opening 14 a of the pictureelement electrode 14. The liquid crystal display device 800 furtherincludes the protrusion 22 b illustrated in FIG. 24B as the secondorientation-regulating structure 28 provided around the center of aregion opposing the solid portion 14 b of the picture element electrode14.

[0285] In the liquid crystal display device 800, the radially-inclinedorientation is stabilized by the orientation-regulating force exerted bythe side surface 40 s of the protrusion 40 and theorientation-regulating force exerted by the surface of the protrusion 22b. Since the orientation-regulating force exerted by virtue of thesurface configuration of the protrusion 40 and the protrusion 22 bdescribed above stabilizes the radially-inclined orientation regardlessof the applied voltage, the liquid crystal display device 800 has adesirable stress resistance.

[0286] In a case where the protrusion 22 b protruding from the counterelectrode 22 into the liquid crystal layer 30 as illustrated in FIG. 24Bis employed as the second orientation-regulating structure 28, thethickness of the liquid crystal layer 30 may be defined by theprotrusion 22 b. In other words, the protrusion 22 b may function alsoas a spacer that controls the cell gap (the thickness of the liquidcrystal layer 30).

[0287]FIG. 30A and FIG. 30B illustrate a liquid crystal display device900 having the protrusion 22 b that also functions as a spacer. FIG. 30Ais a plan view as viewed in the substrate normal direction, and FIG. 30Bis a cross-sectional view taken along line 30B-30B′ of FIG. 30A.

[0288] As illustrated in FIG. 30A and FIG. 30B, in the liquid crystaldisplay device 900, the thickness of the liquid crystal layer 30 isdefined by the protrusion 22 b provided around the center of a regionopposing the solid portion 14 b of the picture element electrode 14 asthe second orientation-regulating structure 28. Such an arrangement isadvantageous in that it is not necessary to separately provide a spacerfor defining the thickness of the liquid crystal layer 30, therebysimplifying the production process.

[0289] In the illustrated example, the protrusion 22 b has a truncatedcone shape as illustrated in FIG. 30B with a side surface 22 b 1 that isinclined by a taper angle θ less than 90° with respect to the substrateplane of the substrate 21. When the side surface 22 b 1 is inclined byan angle less than 90° with respect to the substrate plane, the sidesurface 22 b 1 of the protrusion 22 b has an orientation-regulatingforce of the same direction as that of the orientation-regulating forceexerted by the inclined electric field for the liquid crystal molecules30 a of the liquid crystal layer 30, thereby functioning to stabilizethe radially-inclined orientation.

[0290] As schematically illustrated in FIG. 31A to FIG. 31C, aradially-inclined orientation can be obtained also with the liquidcrystal display device 900 having the protrusion 22 b that functionsalso as a spacer, as with the liquid crystal display devices 600 and700.

[0291] While the protrusion 22 b has the side surface 22 b 1 that isinclined by an angle less than 90° with respect to the substrate planein the example illustrated in FIG. 30B, the protrusion 22 b mayalternatively have the side surface 22 b 1 that is inclined by an angleof 90° or more with respect to the substrate plane. In view of thestability of the radially-inclined orientation, it is preferred that theinclination angle of the side surface 22 b 1 does not substantiallyexceed 90°, and it is more preferred that the inclination angle is lessthan 90°. Even if the inclination angle exceeds 90°, as long as it isclose to 90° (as long as it does not substantially exceed 90°), theliquid crystal molecules 30 a in the vicinity of the side surface 22 b 1of the protrusion 22 b are inclined in a direction substantiallyparallel to the substrate plane and thus take a radially-inclinedorientation conforming with the inclination direction of the liquidcrystal molecules 30 a at the edge portion, with only a slight twist.However, if the inclination angle of the side surface 22 b 1 of theprotrusion 22 b substantially exceeds 90° as illustrated in FIG. 32, theside surface 22 b 1 of the protrusion 22 b will have anorientation-regulating force of the opposite direction to theorientation-regulating force exerted by the inclined electric field forthe liquid crystal molecules 30 a of the liquid crystal layer 30,whereby the radially-inclined orientation may not be stable.

[0292] The protrusion 22 b that functions also as a spacer is notlimited to a protrusion having a truncated cone shape as illustrated inFIG. 30A and FIG. 30B. For example, the protrusion 22 b may have a shapeas illustrated in FIG. 33 such that the cross section thereof in a planevertical to the substrate plane is a part of an ellipse (i.e., a shapesuch as a part of an elliptical sphere). In the protrusion 22 billustrated in FIG. 33, while the inclination angle (taper angle) of theside surface 22 b 1 with respect to the substrate plane varies along thethickness of the liquid crystal layer 30, the inclination angle of theside surface 22 b 1 is less than 90° regardless of the position alongthe thickness of the liquid crystal layer 30. Thus, the protrusion 22 bhaving such a shape may suitably be used as a protrusion for stabilizinga radially-inclined orientation.

[0293] The protrusion 22 b as described above that is in contact withboth the upper and lower substrates (the TFT substrate and the countersubstrate) and functions also as a spacer defining the thickness of theliquid crystal layer 30 may be formed either on the upper substrate oron the lower substrate in the process of producing a liquid crystaldisplay device. Regardless of whether it is formed on the upper or lowersubstrate, the protrusion 22 b will be in contact with both substrates,functioning as a spacer and as the second orientation-regulatingstructure, once the upper and lower substrates are attached to eachother.

[0294] Arrangement of Polarization Plate and Phase Plate

[0295] A so-called “vertical alignment type liquid crystal displaydevice”, including a liquid crystal layer in which liquid crystalmolecules having a negative dielectric anisotropy are vertically alignedin the absence of an applied voltage, is capable of displaying an imagein various display modes. For example, a vertical alignment type liquidcrystal display device may be used in an optical rotation mode or in adisplay mode that is a combination of an optical rotation mode and abirefringence mode, in addition to a birefringence mode in which animage is displayed by controlling the birefringence of the liquidcrystal layer with an electric field. It is possible to obtain abirefringence-mode liquid crystal display device by providing a pair ofpolarization plates on the outer side (the side away from the liquidcrystal layer 30) of the pair of substrates (e.g., the TFT substrate andthe counter substrate) of any of the liquid crystal display devicesdescribed above. Moreover, a phase difference compensator (typically aphase plate) may be provided as necessary. Furthermore, a liquid crystaldisplay device with a high brightness can be obtained also by usinggenerally circularly-polarized light.

[0296] According to the present invention, a liquid crystal domainhaving a radially-inclined orientation is stably formed with a highdegree of continuity. Therefore, it is possible to further improve thedisplay quality of a conventional liquid crystal display device having awide viewing angle characteristic. Moreover, with the use of the firstorientation-regulating structure and the second orientation-regulatingstructure, it is possible to stabilize the radially-inclined orientationand also to fix the position of the central axis of theradially-inclined orientation. Thus, the occurrence of an after imagedue to a stress applied to the liquid crystal panel is suppressed.

[0297] While the present invention has been described in a preferredembodiment, it will be apparent to those skilled in the art that thedisclosed invention may be modified in numerous ways and may assume manyembodiments other than that specifically set out and described above.Accordingly, it is intended by the appended claims to cover allmodifications of the invention that fall within the true spirit andscope of the invention.

What is claimed is:
 1. A liquid crystal display device, comprising: afirst substrate, a second substrate, and a vertical alignment typeliquid crystal layer provided between the first substrate and the secondsubstrate; and a plurality of picture element regions each defined by afirst electrode provided on one side of the first substrate that iscloser to the liquid crystal layer and a second electrode provided onthe second substrate so as to oppose the first electrode via the liquidcrystal layer, wherein: the first substrate includes a firstorientation-regulating structure in each of the plurality of pictureelement regions, the first orientation-regulating structure exerting anorientation-regulating force so as to form a plurality of liquid crystaldomains in the liquid crystal layer, each of the liquid crystal domainstaking a radially-inclined orientation in the presence of an appliedvoltage; and the second substrate includes a secondorientation-regulating structure in a region corresponding to at leastone of the plurality of liquid crystal domains, the secondorientation-regulating structure exerting an orientation-regulatingforce for orienting liquid crystal molecules in the at least one liquidcrystal domain into a radially-inclined orientation at least in thepresence of an applied voltage.
 2. The liquid crystal display device ofclaim 1, wherein the second orientation-regulating structure is providedin a region corresponding to a region in the vicinity of a center of theat least one liquid crystal domain.
 3. The liquid crystal display deviceof claim 1, wherein in the at least one liquid crystal domain, adirection of orientation regulation by the second orientation-regulatingstructure coincides with a direction of the radially-inclinedorientation by the first orientation-regulating structure.
 4. The liquidcrystal display device of claim 1, wherein the first electrode includesa plurality of unit solid portions, the first orientation-regulatingstructure including the plurality of unit solid portions, so that when avoltage is applied between the first electrode and the second electrode,an inclined electric field is produced along a periphery of each of theplurality of unit solid portions, thereby forming the plurality ofliquid crystal domains in regions respectively corresponding to theplurality of unit solid portions.
 5. The liquid crystal display deviceof claim 4, wherein a shape of each of the plurality of unit solidportions has rotational symmetry.
 6. The liquid crystal display deviceof claim 5, wherein each of the plurality of unit solid portions has ashape with an acute angle corner.
 7. The liquid crystal display deviceof claim 4, wherein the second orientation-regulating structure isprovided in a region corresponding to each of the plurality of liquidcrystal domains.
 8. The liquid crystal display device of claim 4,wherein the second orientation-regulating structure exerts anorientation-regulating force for orienting the liquid crystal moleculesinto a radially-inclined orientation even in the absence of an appliedvoltage.
 9. The liquid crystal display device of claim 8, wherein thesecond orientation-regulating structure is a protrusion protruding fromthe second substrate into the liquid crystal layer.
 10. The liquidcrystal display device of claim 9, wherein a thickness of the liquidcrystal layer is defined by the protrusion protruding from the secondsubstrate into the liquid crystal layer.
 11. The liquid crystal displaydevice of claim 10, wherein the protrusion includes a side surface at anangle less than 90° with respect to a substrate plane of the secondsubstrate.
 12. The liquid crystal display device of claim 8, wherein thesecond orientation-regulating structure includes a surface having ahorizontal alignment power provided on one side of the second substratethat is closer to the liquid crystal layer.
 13. The liquid crystaldisplay device of claim 4, wherein the second orientation-regulatingstructure exerts an orientation-regulating force for orienting theliquid crystal molecules into a radially-inclined orientation only inthe presence of an applied voltage.
 14. The liquid crystal displaydevice of claim 13, wherein the second orientation-regulating structureincludes an opening provided in the second electrode.
 15. The liquidcrystal display device of claim 1, wherein: the first electrode includesat least one opening and a solid portion; and the firstorientation-regulating structure includes the at least one opening andthe solid portion of the first electrode, so that when a voltage isapplied between the first electrode and the second electrode, aninclined electric field is produced at an edge portion of the at leastone opening of the first electrode, thereby forming the plurality ofliquid crystal domains in regions respectively corresponding to the atleast one opening and the solid portion.
 16. The liquid crystal displaydevice of claim 15, wherein the first substrate further includes adielectric layer provided on one side of the first electrode that isaway from the liquid crystal layer, and a third electrode opposing atleast a portion of the at least one opening of the first electrode viathe dielectric layer.
 17. The liquid crystal display device of claim 15,wherein the at least one opening includes a plurality of openings havingsubstantially the same shape and substantially the same size, and atleast some of the plurality of openings form at least one unit latticearranged so as to have rotational symmetry.
 18. The liquid crystaldisplay device of claim 17, wherein a shape of each of the at least someof the plurality of openings has rotational symmetry.
 19. The liquidcrystal display device of claim 15, wherein the secondorientation-regulating structure is provided in a region correspondingto each of the plurality of liquid crystal domains.
 20. The liquidcrystal display device of claim 15, wherein the secondorientation-regulating structure is provided only in a regioncorresponding to one or more of the plurality of liquid crystal domainsthat is formed in a region corresponding to the solid portion of thefirst electrode.
 21. The liquid crystal display device of claim 15,wherein the second orientation-regulating structure exerts anorientation-regulating force for orienting the liquid crystal moleculesinto a radially-inclined orientation even in the absence of an appliedvoltage.
 22. The liquid crystal display device of claim 21, wherein thesecond orientation-regulating structure is a protrusion protruding fromthe second substrate into the liquid crystal layer.
 23. The liquidcrystal display device of claim 22, wherein a thickness of the liquidcrystal layer is defined by the protrusion protruding from the secondsubstrate into the liquid crystal layer.
 24. The liquid crystal displaydevice of claim 23, wherein the protrusion includes a side surface at anangle less than 90° with respect to a substrate plane of the secondsubstrate.
 25. The liquid crystal display device of claim 21, whereinthe second orientation-regulating structure includes a surface having ahorizontal alignment power provided on one side of the second substratethat is closer to the liquid crystal layer.
 26. The liquid crystaldisplay device of claim 15, wherein the second orientation-regulatingstructure exerts an orientation-regulating force for orienting theliquid crystal molecules into a radially-inclined orientation only inthe presence of an applied voltage.
 27. The liquid crystal displaydevice of claim 26, wherein the second orientation-regulating structureincludes an opening provided in the second electrode.
 28. A liquidcrystal display device, comprising: a first substrate, a secondsubstrate, and a vertical alignment type liquid crystal layer providedbetween the first substrate and the second substrate; and a plurality ofpicture element regions each defined by a first electrode provided onone side of the first substrate that is closer to the liquid crystallayer and a second electrode provided on the second substrate so as tooppose the first electrode via the liquid crystal layer, wherein: thefirst electrode includes, in each of the plurality of picture elementregions, a plurality of openings and a plurality of unit solid portions,each of the unit solid portions being surrounded by at least some of theplurality of openings; and the second substrate includes anorientation-regulating structure in a region corresponding to at leastone unit solid portion among the plurality of unit solid portions andthe plurality of openings.
 29. The liquid crystal display device ofclaim 28, wherein a shape of each of the plurality of unit solidportions has rotational symmetry.
 30. The liquid crystal display deviceof claim 28, wherein the orientation-regulating structure is aprotrusion protruding from the second substrate into the liquid crystallayer.
 31. The liquid crystal display device of claim 30, wherein athickness of the liquid crystal layer is defined by the protrusionprotruding from the second substrate into the liquid crystal layer. 32.The liquid crystal display device of claim 31, wherein the protrusionincludes a side surface at an angle less than 90° with respect to asubstrate plane of the second substrate.
 33. The liquid crystal displaydevice of claim 28, wherein the orientation-regulating structureincludes a surface having a horizontal alignment power provided on oneside of the second substrate that is closer to the liquid crystal layer.34. The liquid crystal display device of claim 28, wherein theorientation-regulating structure includes an opening provided in thesecond electrode.